Hell,a wife beater and jeans look fine...some kind of chain/necklace and a chain/bracelet(on your left hand)would work well.A regular black sweatband/armband would look neat on your right hand.Boots go well with jeans and sneakers go well with all other pants(like cargo's e.c.t).

Remember your going to be behind your guitar,so try to make contrast with it(your clothes in the pic do.)

Also,dont be afraid to wear your favorite 'band' shirt...people take intrest in what bands other band members like.bands,bands,bands!AHHH!

good luck dude!