This is a classic technique which certainly provides some potential for mind blowing trippiness. If you are willing to go with it and can loosen the knots in your mind sufficiently, you might be surprised at how far out this can take you.
My experience with this is that it goes from this kind of impressionist thing to very pronounced flipping of light and dark with energetic phenomena in the space around your reflection... and then it breaks into an experience of having your face melt away to be replaced by another, and then another, and then another. Often dozens of different faces come up, and the disconcerting thing that usually inspires people to break it off is that the eyes and personalities looking back at you do not feel like your own. It is no longer a reflection of you, but rather a face to face encounter with other beings who regard you in various different lights.
Many texts indicate that these are alternate reality versions of yourself, or in prosaic tomes "past lives." There does seem to be some connection to the people that appear, though I can't say for sure what that is. I mostly (almost exclusively) see other male humans, but occasionally women appear as well as true alien lifeforms. The human looking people could be ETs as well (if they live in alternate universes, they are extra-terrestrial)... who knows? At a certain point, having a stare off with a bug faced being of limited friendliness becomes a bit much, and the mind naturally begins to wonder if the other people might not be able to reach across the dimensions to do something more than gawk.
Another interesting note on this is that it can be done with another person and not just a mirror. Sitting comfortably in a lotus or other posture one can maintain for a good amount of time with a candle in between you can produce similar effects, only the feeling is that you are looking into the multiple incarnations of the other person while they meet yours.
Not for the faint of heart.
The distances can be dialed in to increase this effect, but the candle is nearly always best halfway between you and the mirror (or person).
The last thing I will say about this technique is that it can be quite interesting once it is going strong to shift away from the locking eyes thing and observe the environment over the other entity's shoulder. You might be surprised to find that the room behind them is equally alien. It takes a bit of practice to shift the attention without breaking the connection and spoiling the effect.
I will respond to OBE, WILD and AP methods later in this thread. If you can't wait, there are a number of threads already around in which we have discussed this subject in great detail (as well as argued the subject to the ground). Search the forums for "astral lucid" under posts and a bunch of these threads will come up. You can click over to a thread and then start from the beginning.