well, first of all, you don't want to be uncomfortable. so you don't want to go so far outside of your norm that you feel inordinately self-conscious. so if you're used to wearing jeans and a t-shirt, i would probably stick with jeans. dark skinny jeans are good for looking slightly less casual if you pair them right. then choose a nice blouse that makes you feel pretty. give your hair some attention, whatever style you like, just make sure it looks polished and not sloppy. light makeup and some cute flats (i'm assuming heels would be uncomfortable for you, but if you're used to wearing them, they're good as well) and you're good to go.