How can Buddhism help with bad habits?

Yes, mindfulness helps. The question has been technically answered in depth here also:

https://buddhism.stackexchange.com/a/19888/13383

Being angry and abusive is also a habit, and it is highly addictive if overly cultivated. One example is to live more mindful life and mindfully observe that anger that leads to abuse, note that anger is within me and shift your attention to the breath, as just as all phenomena such as backache or itching - it will naturally subside.

Watching breath has also another characteristic which is calming the mind; and that is the only state when one can think clearly with illuminating clarity, not under any influence.

Maybe you find one of those videos helpful. https://www.youtube.com/playlist?list=PL4j9bs3T1aPR6nBjUsHy1dns3A9ZjqjoY

The one about p**nography and masturbation handles the question about addiction quite well, imho.

Apart from using mindfulness-based techniques as found in other answers, you can also try the following contemplation from AN 5.57:

“And for the sake of what benefit should a woman or a man, a householder or one gone forth, often reflect thus: ‘I am the owner of my kamma, the heir of my kamma; I have kamma as my origin, kamma as my relative, kamma as my resort; I will be the heir of whatever kamma, good or bad, that I do’? People engage in misconduct by body, speech, and mind. But when one often reflects upon this theme, such misconduct is either completely abandoned or diminished. It is for the sake of this benefit that a woman or a man, a householder or one gone forth, should often reflect thus: ‘I am the owner of my kamma, the heir of my kamma; I have kamma as my origin, kamma as my relative, kamma as my resort; I will be the heir of whatever kamma, good or bad, that I do.’

When I was younger I used to identify with my anger to a very strong degree. You see, I had a very bad temper. It was so bad that I regularly scared the people around me when I lost it. When I was in grade school I was known for my temper. It was an integral part of my reputation and my own self-assessment. Other children would get afraid when I absolutely lost it and I absolutely lost in on many an occasion. My family generally agreed that I received my temper from my father who was also infamous for having a very hot temper.

I idealized my father when I was young and used to follow him around. And then when I was four to five years old, my father left me. I think this likely played a large part in my strong attachment and self-identification with my anger. I loved my father and I received this from him and when he left it was one of the ways I internalized a continuing connection with him.

I used to think of my anger as a very big part of who I was and even considered it a source of refuge. Cringe :( I thought it protected me from others and I saw it as a way I could impose my control and will over others. Or so I thought...

After I started studying Buddhism and talking about this with my teacher she instructed me to have a good look at this anger and to watch carefully the effect it had on myself and others. I understood in the abstract maybe that anger was bad, but it was such a basis for my conception of self that I did not really think it was possible to get rid of it. Even worse I was scared to do so and didn't want to! If I abandoned this wouldn't I be abandoning a part of myself?? Luckily, I listened to my teacher and checked up on it and used a little bit of mindfulness to see what the real fruits were of my anger...

Let's just say that over the course of a few years it became quite apparent to me that - shockingly - there was not a single redeeming quality to my temper. To my surprise, after looking carefully I found that my temper was a huge hindrance and caused me a huge amount of grief. It was also a very large source of suffering for those around me. This really did come as a surprise! I'm ashamed now to say that this was a surprise, but it really was...

After developing sure knowledge that my temper was a problem and was only causing me grief - without a single redeeming quality!! - I started to wonder how I could abandon it? I was still very unsure if this was even possible given how long I had self-identified with it. It was a very large part of who I thought I was.

The first thing I did was to start thinking and resolving that I was not my anger. My anger was not an integral part of me, but rather a construct and habit that I had developed. After looking into my past and coming to terms with my father and other formative developments I can say that I no longer identify with my anger at all. To be clear, I still get angry... but it is no longer a part of my self-conception.

Really, it is quite amazing to me how far I've been able to come in abandoning anger. That has more to do with just how bad my temper was than how little anger I have now ;) It is all relative after all. The keys were to understand what a burden my anger was and to realize that I am not an inherently angry person. I cultivated the wish to get rid of and abandon my temper. I watched when it would arise and would generate regret at doing so and would resolve to try harder to be mindful. I started to associate my anger as a bad little habit of mind. Nothing more. One that just need to be watched carefully lest it cause damage to myself and others. And lo and behold, while I'm far from perfect I really have made huge progress! I've greatly reduced the suffering I've inflicted on myself and others from my temper.

So this is my story and experience trying to abandon this habit of anger. It really is a kind of thought training and practice if you think about it. There is no magic to it just a lot of practice and reflection.

My current big project is my arrogance. That is another habit that I've self-identified with and have stupidly cultivated over the years. The headway I've made with my temper though gives me confidence that arrogance can also be abandoned. The technique I'm using right now which seems to be really helpful is to reflect whenever I do something well or receive praise and the arrogant mind arises, "Oh silly arrogant mind! You played no part in giving cause to whatever success I just achieved. In fact, I achieved that success in spite of you and certainly not because of you! You didn't help me in the slightest to achieve this so - arrogant mind - you deserve none of the credit. Now go back to playing in your sandbox you silly arrogant mind!"

So, something like that... :)

Hope this helps!

Buddhism is of great help in dealing with addictions. I will address the smoking and drinking ones. This is how my teacher advised me to deal with.

The following answer is not to promote smoking in any way, it's just based on an acute understanding on how difficult it is to go cold turkey on addictions.

Smoking Awareness

You have to basically remember that the whole process is about mindfulness and awareness and your will to quit the habit. Whenever the desire arises don't smoke while talking to friends or other people then you are not aware of smoking. Then retreat into solitariness. Take out the cigarette and smell it before lighting it, feel it, then lite it mindfully, take in every puff and exhale every puff with an articulate concentration of what exactly you are doing. At an end of each cycle contemplate that death has come one breath closer. Contemplate the gory death with cancer or any other terrible disease you are going to suffer. This contemplation creates a repulsion. Plus the more mindful and aware you become, the more you feel the smoke and the smell of cigs repulsive. This heightened awareness of smoke takes you to that state of mind you once had as a child or teenager when you hated smoke. The more aware and sensitive you become the more you don't want to do it anymore.

Also if you start practicing Vipassana you like the feeling of simple breath and you start knowing how blissful the breath is, so what happens is you start not wanting to smoke anymore.

If you study the 10 Paramitas and 8 fold path you start to know to have compassion towards your self as well and not to harm yourself anymore.

Within the context of Buddhism, you want to quit smoking as not to do the bad karma of harming yourself without feeling guilty about it.

Alcohol Awareness

Just like smoking try to be aware of every gulp of alcohol you will have. Then with awareness, you observe how the head gets heavy, you observe how you start feeling tipsy, you observe how you lose the mind and how evil thoughts overcome you. If you practice Vipassana you will learn to observe, you extend that same capacity to observe yourself while drinking. This will eventually create the repulsiveness. You don't want to be addicted to alcohol anymore.

Abusive behavior

Within the context of Buddhism, you start practicing Metta meditation i.e. compassion and kindness towards all beings, as this practice will grow, it will be hard to be abusive towards people also it will create forgiveness towards yourself and others in you.

Buddhism helps a lot overcoming bad habits

Telling yourself 'The self is false' or 'bad' won't make a difference in your day-to-day life because these are just intellectual understandings without any underlying experience, therefore you don't really FEEL what you are telling yourself.

If you have harmful addictions that are long manifested Buddhism is probably not the best solution. In my opinion, Therapy which targets your both your thinking and behaving is most suited (Cognitive Behaviour Therapy/Acceptance Commitment Therapy etc.)

Ingrained habits were practised for a long time and reducing or even overcoming them can take a long time and that's why goal setting, coping skills, cost benefit analysis, restructuring 'distorted' cognitions and alternative behaviours are critically important.

While practising kindness can undermine abusive and angry behaviour(s) it only surpresses it for a while but the perceptions of anger/abuse are still there. Trying to be kind or compassionate in a difficult situation to the other person is really hard and you better be patient in such situations or delay the situation for a couple of minutes to think through your behaviour (even this is really hard).

In the end, it is very important to have self acceptance towards yourself, which means that you never judge the doer but the acts you have done and you do so in a constructive and kind manner.

My first Buddhist teacher was extremely helpful with this. Basically, he explained that all these problems come from attachments. "Ego" is just a name for a tangle of attachments. Someone says something that goes against your attachment and you get triggered. You think "this is right, this is the way its supposed to be - and what they did is wrong". That "supposed to be" is the attachment. They are like mind worms, you should get rid of them. If you start now, in five years you will have none. Just don't get angry at people who still have attachments, because that's an attachment too. Makes sense?

It's called "attachment" because you think this is the only right way it should be - but in reality it's not the only way. Nothing in the world has to be one way. Letting go of attachments involves catching yourself getting triggered, identifying the attachment, and then expanding your perspective to include other possibilities. This process goes deep, very very deep - until you completely lose all shape, any ground under your feet - so it's is not for the faint of heart. Following this path is like a robot disassembling itself, piece by piece - until there is nothing left. That "nothing" is freedom.

Attachments are the real issue. Addictions are secondary, just a side effect.

What's kinda interesting and cool is that reality you find yourself in is always the reverse projection of your hidden attachments. It's really amazing. The circumstances and the overall mood of the situations that you get in, is a reflection of your attachments. So the more you hold on to them, the worse it gets - and as you let go, a different reality is assembled around you.