Details when practice vipassana

Mindfulness is not intellectualizing or analyzing. Such distinctions as 'sweet', 'salty', 'good', 'bad', actually inhibit mindfulness by reifying the self. Mindfulness is more synonymous with awareness. This awareness expands in every direction as you advance your understanding of sunyata. Mindfulness is a natural expression of this wisdom. If you get lost in thought or analysis of experience, that is not mindfulness. That is more of your ego polluting experience with distinction.

This is why paradoxically, you can't really "try" to be mindful. When you do try, you end up being sabotaged by your ego/intellect.

Yuttadhammo is correct. It is better to bias yourself towards noticing the ultimate same-ness (anicca, anatta, dukkha) of the particular experience rather than to get involved in being attracted or repelled by the content (specific taste, specific type of imagination) by investigating it and analyzing it. Treat all experiences as ultimately the same and detach yourself from feeding them energy.

I highly reccommend the instructions on page 14 of this meditation manual. It is the best, most amazing, integrative gem of a manual on vipassana and one should read the whole thing.

Here's the excerpt relevant to the fine, content-free nature of vipassana practice:

1 First, sit comfortably to relax your body and your breathing. We call this first step of meditation the "preparatory practices", or physiological adjustments, for tuning the physical nature. Basically, you want to situate yourself so as to lessen any physical disturbances or distractions. Then after your body is calmed, you start quietly observing your inner thoughts and emotions. In other words, you simply watch your internal psychological functions like a third person observer. This third person doesn't interfere with what's going on, or participate in the activities they're observing. He just stays there watching, neither rejecting or clinging to anything; he simply sits there silently observing.

[2] You continue watching your internal process of mentation until you reach the point where you can clearly observe every thought and idea which appears in the mind without any vagueness or ambiguity. Naturally, you are not tightening your body nor mentally straining during this practice. Rather, you always remain relaxed while clearly observing your internal mental processes. After a while, you will eventually be able to distinguish that the process of mentation has three parts: a preceding thought which has gone, a thought which has not yet arisen, and the immediate clear radiance, or mental state of present mind. With continued watching, the separation of these three states becomes quite clear.

[3] With continued observation, you progress a bit further and next realize that the past, present and future thoughts never stay. Since they don't stay they can never be grasped, hence we say that "fundamentally, they have no base to rely upon". Observing the appearance and disappearance of thoughts is called "observing birth and death", for the coming and going of thoughts is a ceaseless, never-ending process of arising and then disappearance, or decay. This is the realm of birth and death. By observing this stream of birth and death, you will gradually learn how to detach from the mental processes, and you will become more familiar with the false mind of consciousness. In other words, you will be able to drop the illusion that our mental process is a fundamental reality. Rather, you will gradually see that all mental states are ungraspable, transient phenomena which come and go without end, and they're more like insubstantial bubbles of foam or particles of dust which have no fixity of nature. Because of their ceaseless birth and death and the gap in-between, what we normally imagine as a continuous continuity of thoughts is actually an illusion, like the unbroken wheel of light we see when a stick of fire is spun in the air. Thus through this process of inner watching, you will begin to realize that our mental state is an ongoing process separate from our true self. The true self is what's watching this play scene, so it's like an internal knower who never moves. If you go from here to the North Pole and back, the scenery always changes, but that inner knower never changes--it never moves. In fact, it never leaves, and has never come either. It just is. That's what we're seeking, though on a more profound level than we can explain here. Now in watching thoughts without adding any energy to the process, you'll begin to understand how dreamlike our consciousness actually is because the reality it gives birth to seems to be there and yet the concreteness of this reality is absent. It isn't real. Phenomena are empty and yet they are conventionally real, but this conventional reality is also empty. So eventually, through observation with detachment, you'll reach the stage where you can mentally relax while "giving birth to the mind without abiding anywhere". Through continued observation you will notice that thoughts or phenomena ("existence") are born from emptiness (mental silence), and the existence of emptiness relies on phenomena. Existence and emptiness are both manifestations of one nature--its single source, our true self--so on the road of cultivation you don't cling to either side. Both sides are phenomenal constructions, or false relativities, so both sides are not real. Hence in shamathavipashyana practice, you start to contemplate the mean between stillness and activity. In practicing this inner watching, you'll get progressively better at becoming mentally free because you'll stop clinging to or rejecting your thoughts, emotions and sensations. Thus your mental awareness will increasingly "open" and your ability to function in the world will increase as well, so you'll actually be expanding your awareness while saving a lot of energy that you'd normally waste in useless clinging. Furthermore, your internal state of peace and calm will progressively develop with every increase in clarity. Thus if you keep observing the origin and destruction of thoughts while paying particular attention to where they come from and go to, you'll eventually obstruct the stream of consciousness.

[4] With the stream of consciousness disrupted, you will then notice a momentary gap of stillness, or silence, between all your thoughts. In other words, if you practice this method of inner observation for a long time--by wordlessly watching thoughts without injecting energy into the thought stream--the process of silent observation will itself disrupt the stream of mentation. The state of mind in the immediate present will gradually open up to reveal a tiny gap of mental quiet, or emptiness; when a previous thought has disappeared and a subsequent thought has not yet arisen, the mind will seem quiet. This mental silence is not a gap of dullness nor stupor, nor should it be a forced silence or blankness you create through suppressing thoughts. Rather, it will be a lucid, clear and open awareness, and these characteristics will gradually unfold as more time is spent in this state. In other words, after quietly observing our mental processes for quite some while, one will notice a tiny gap of silent pausation between thoughts which we refer to as "cessation". If we continue observing this state without effort and shine awareness on it, it will gradually expand further and further. Looking into this gap of silence is the process of "contemplation" or vipashyana. It's a quiet realm similar to emptiness, but it still isn't the genuine emptiness of Tao. Nevertheless, this is what we're initially after because we can use this state to begin cultivating prajna wisdom.

[5] If you continue to carry over this state of watching the mind (the process of silent detachment and immediate awareness) during all your normal activities--whether walking, talking, sitting or sleeping-- you'll be able to reach the point where thoughts no longer bind you. Gradually their volume will die down, your radiant awareness will expand and you will be able to seamlessly enter into the real emptiness of samadhi. In other words, if you keep observing the state of cessation by shining awareness on this state, you will eventually arrive at dhyana. Thus the practice of shining awareness on the silence within is commonly referred to as "contemplating mind". If you continue progressing in this manner by reaching further levels of emptiness and shining wisdom awareness on any state of cessation you reach, you will eventually acquire prajna wisdom, or transcendental wisdom. Then you'll climb the various ranks of samadhi and enter into the Tao. (Twenty-five Doors to Meditation: A Handbook for Entering Samadhi, William Bodri and Lee Shu-Mei (Samuel Weiser, York Beach: Maine, 1998), pp. 14-17)

Also, I would refer to the chapter on vipassana practice in Daniel Ingram's book. It says the same thing yuttadhammo and I said with some vivid analogies.