There is a beautiful simplicity when you're playing a bluff. Essentially, this is that THE CARDS IN YOUR HAND ARE ALWAYS THE NUTS. You can represent anything, so you'll be wanting, at one point or other, to represent the best hand possible so others will fold.

So, pre-flop, you have The Nuts; on the flop, you have The Nuts; on the turn and the river, you have The Nuts. Feels good, huh? So bet accordingly.

Second tip - any low-level player with a made hand will call your bluff bet on the river nine times out of ten, often including all ins. So don't leave your bluff till the river unless you have a damn good reason for doing so.