Don't suffer in stiletto heels when you'd rather wear flats. And don't suck in your stomach to squeeze into a skin-tight pair of designer jeans. Wear what makes you comfortable.
If you're not sure what makes you comfortable, look to your closet for inspiration. Sift through your clothes and pull out your favorites. Ask yourself why you love them. Do the fabrics feel good on your skin? Do you like the way the clothes make you look? Do you get a lot of compliments when you wear them? Use those favorite pieces as a springboard when you shop for new looks.
Speaking of shopping, don't just rush in and out of stores -- take time when you're trying on clothes. Consider the ease of putting on the article of clothing, how good you look in it, and how well it fits in with your current wardrobe and needs.