I use whatever rankings are available from the website I am drafting on. Otherwise I draft off an ADP cheatsheet that is closest to what my competition is going to use.
Then whenever I see a player I want coming up on the cheatsheet, I make sure to grab them. IF there is someone I really want, I will grab them a round or two early. A lot of times, I have 3 or 4 players that I consistently grab "a round early" because I see something in them that other people generally don't.