Hi chic chic,
I'll tell you what has helped me in slowly trying to build a wardrobe after years of either neglecting it- or running out desperately, spending money on things I would then never wear.
-Angie's advice on pretty non-t-shirt tops. I discovered I feel so much better about myself in a pretty top or blouse as opposed to a blah t-shirt.
-Great jeans.
-casual shoes that aren't sneakers, but you can still play in. This has been hardest for me. I fell into the easy-on clogs rut, and I'm still weaning myself off of them.
-depending on where you live, a wonderful outerwear piece. I'm in Seattle, and a good all weather coat is a basic. Might as well be one that looks fab.
I would get into trouble when an event would come up and I'd have nothing to wear to it. I'd end up with a panic piece bought the day before, spent more than I should, and it would never get worn again. So, my goal is to have the pieces already there for: date night, day wedding, dressy auction event, etc. Less stress, better style!
Good luck!