1) probably the eaiest way for me is nightmares ( i noticed somone else posted it) Usually in nighmatres for me im constatly trying to find a way to get away or find something to fight the "monster" with, usually if you do something will appear and then you can stop and think "where did that just appear from?" Another thing i do is if im running i tend to hop..usually if you do so you will get this..kind of gut feeling and you notice you get this gut feeling sort of...and you might be jumping higher the normal..then you really notice if somethign is different (normal people don't jump 10 feet above the ground =p)

2) Listening to music. I noticed this helped out, usually i have it playing lowely and you just concentrate , kind of sing with it or get in to it..slowly you will feel different and notice that images created by the song will start popping in to your head, great way to notice your starting to dream.

3) sleeping in a different position. Hey it might sound where but if you try it and feel the urge to flip or turn, dont! just put up with it. Slowly but surely you will get used to it and then you will start feeling your body kind of shut down almost, another way you know your about to dream.