What are do's & dont's which should be followed for serene & calm life?

Thank you for your deeply thought out question. I have been looking at the Buddhist Stack site for a little while, and I notice some real similarities in the way many of the questions are formed. So, first , it is good to study, by which I mean get a perspective of the landscape, in this case the Buddha's Dharma. Think for yourself. If someone tells you to jump of a cliff, you probably will not, Thank God, for that.So , when this hypothetical person told you to jump , what happened? you had an insight that there would probably be a bad result. So, the Buddha was quoted as saying do not believe any think he tells you , until you have tested the truth of that saying and the possible benefit of that idea for you to apply. So, much for that , for now. So you study, then you get the big picture and you actually start to see how using your mind in a certain way is much more beneficial that using your mind in another way. This is the beginning of good judgement. So, Here's the biggie. Cease to do Evil, Learn to do Good, remove all defilements , follow this way to Compete, total, supreme Enlightenment. So, How do I stop doing evil, well , let's start on the simplest level. What if you determine that to get really frustrated and angry and nervous about what just happened to you is not good. So , then , you go to a quiet place or find some friends and calm down. This is ceasing to do evil and learning to do good.So now, you might have gotten a little , "good idea" . If you keep doing this , with all your experiences, you will learn to relax, and better still , you will say. "Oh, I am relaxed now, that is better that going crazy." What if I start to develop some real concentration. I bet I could do this even better, and maybe, just maybe, I could help someone else learn to become happier, too. And so on. Of course there is much more. Good Luck.

Shamelessly stolen from Dhammadhatu's great answer:

Practise friendliness, compassion, appreciation for goodness & equanimity.

In my personal experience, this is really the make-or-break-factor. It is the one thing which you can positively, actively influence daily, nay, in each moment. It needs no study of any text or "rules".

It can often be very easy, but sometimes very hard, which means you can often practise it, and sometimes learn very much from it.

This includes being nice to your enemies, loving people who would be hated by others, appreciating things other people do which would otherwise seem unappreciable to you, and so on. All of these things are not obvious if you really think them through, but they are possible.

It is very important that what you do to achieve this goal is not running around with a constant insincere smile, but the feelings expressed above need to be real. You need to really see what is good about someone who seemingly is "out to get you", or someone who is "stupid", and so on. This is the hard part, which will lead to your personal development. But it is noticeable.

There is some quote about Marilyn Monroe, visiting some GIs in Vietnam, where some guys said that she had such an overwhelming presence not because she was beautiful, a goddess even, but because she sincerly made everyone feel liked and "on the same level". That's the kind of quality you're looking for.

Another example would be if you were to be attacked - your goal would be to be able to defend from attacks, but in a way that really is good for the attacker. You would not want to "break" or kill your attacker. But you would also try, while "winning" decisively, to leave him with his honor intact, or, better yet, find ways so that you both can win and there is no loser at all.

Equanimity obviously entails that you keep your calm in difficult situations, and not only by suppressing your anger, but by really letting the stressfull things "pass through" without letting them harm you. There is a lot of mind work you can do to achieve that.

Observing the "five precepts" is the starting point.

The five precepts are the "don't do" things (the things to avoid). Then you have to practice things to do -- I ask people in my meditation group not only to observe the five precepts but also practice the opposite. That is:

1. Killing vs loving kindness
2. Stealing vs generosity
3. Inappropriate sex vs refrain
4. Lying vs telling the truth
5. Alcohol vs practicing mindfulness