If you don't have many curves, you can create some by wearing a one-piece swimsuit with a high-on-the-thigh cut. A belted waistline on a one-piece suit will give the appearance of a whittled middle. You can also wear a draped, surplice detail that pinches in at the waist or a curvy seam line that runs down each side of the torso.
Bikinis are also good for you. You can add some illusion at the hips with rings, ruffles and bows. If you're small on top, go for a strapless bandeau. Go with a dark, solid bottom and a wildly printed or embellished top.
You should avoid solid colored or horizontal striped one-pieces.