First chuck any which do not fit or flatter you, any which are permenantly stained or have holes/ tears.
Whatever's left i'd work on the "have i worn it in the last 12 months" theory and does it work with the other things in your wardrobe x

Loulou gave you the best advice - be ruthless on the unflattering, stained or faded items. It's ok to keep one or two for sentimental reasons but you want to keep your emphasis on what looks great.

Whenever you purge an overly-large collection of anything, it's also a good idea to do some thinking about how you got there in the first place: "What am I doing that has resulted in my having two drawers full of tees that I don't wear?" It could be buying things that turn out to be unflattering, having trouble passing up a sale, anxiety about letting things go, etc.

Once you figure that out, you're well on your way to not ending up in the same place six months from now...

Do you want to post some photos and have us help with the "what to keep" decisions?

Yay! I love it when people get stuck into wardrobe editing. I have a category devoted to purging and closet organization. Have a squizz right till the end:

http://youlookfab.com/category.....anization/