I too am very tight. I read Harrington's books,"Harrington On Holdem" and have discovered how to raise that aggression. You must be patient, keep playing your game, set a table image, and then you can use that table image to make moves, steal pots, and win more pots easily.
You must be careful not be too aggressive as that can give an image of a loose player and you will be called when you don't want to be.
It takes some practice, at least it did for me, to change one's style.