Try to pay attention to perceived effort, keeping it steady.
Keep your pedal stroke smooth. You will be shocked and amazed at how concentrating on form will improve your climbing ability.
I find that thinking about using my hamstrings makes me use them. It's good to use as many leg muscle groups as you can to attack a hill.

A lot of people oooh and aaaah over Lance's climbing technique. In fact, it does work, with a lot of practice. If you're a big guy like Ullrich or stocky like Botero, you'll find that ticking over a large gear might work for you. Again, this technique takes practice too.

Remember to shift back and forth between standing and sitting. Keep in mind, you have to do what feels right. Just because the guy next to you stands, doesn't mean you should. After all, your pedal stroke is more efficient when sitting.

I always find that psychological tricks like saying "it doesn't hurt that bad" help me a lot.