There was a period of time not so long ago when I was going through a horrible cold spell. It started with an extreme run of bad luck, big favorites getting drawn out on repeatedly. Invariably, this had an effect on my game, as I suddenly became much more passive. Instead of forcing them to make bad plays without the odds, I was letting them off cheap, and then paying them off.

One of the things I did to correct this was to find a perverse sense of joy in bluffing a hand. For my personality, this wasn't a very difficult thing to force myself to do - I think I'm smarter than everyone else, and nothing beats profiting on the misfortune of others - but I really focused on it. Of course, I had to make sure I kept myself in check, and did not let this get out of control.

I think for any player, there is a way you can safely force yourself to become more aggressive at the table. You just have to find that one out on your own.

Yeah, sorry for the cliche there at the end.

Oh, and locutus' advice is also very good.