I used to just stand as soon as there was a hill, and then just stomp my way up it, but this only works with smaller hills that are common around boston.
Just a week or two ago, I realized that it is better to stay seated, and power up that way, and maybe get out of the saddle and throw the bike back and forth near the crest of the hill. I only really ride small hills though, as they're aren't many hills around boston where I normally ride.