i work @ a clothing store. it's not too hard, really. i doubt your boss will be able to figure out from you initially how good you are socially...
it's not too hard though. you just need to be willing to help people and ask how you can help them, be engaged in their convarsation and care about what they're looking for, know your stuff about w/e you're selling, give opinions, be friendly to the other employees, that sort of thing. care about the people, and be friendly! it's not too hard, i swear! just don't make your boss hate you, like don't be offensive or rude or anything like that. always do as you're asked. don't make you're breaks too long, and drink coffee beforehand (headaches are TERRIBLE on the job)! !!
it's really not that hard. just pick a store that applies to your interests and you'll meet people like you and be able to relate to them well. plus, i'm sure you'll get good discounts! it will be fine!
also, work somewhere really low-stress, like a little shop. it will mean less pressure if that's what you're worried about