This is a difficult question to answer since there are so many different body types and swimwear available.  However, whether you’re male or female, two things you should always keep in mind when it comes to buying flattering swimwear:  accentuate the positive, and downplay the negative.
For example, if you want to accentuate your long, muscular legs, swimwear that has a higher cut on the thigh is your best bet.  If you rather focus on your narrow waist, a swimsuit that is structured, with fashion that draws the eyes towards the waist is a good choice.  If you’d rather not have people notice a more robust bust line, then consider a swimsuit that highlights other aspects of your body.
However, the most important thing to do when searching for a flattering swimsuit is to make sure that it fits your body well.  If you’re female, take into account your bust size, the length of your torso, and your waistline.  If you’re male,  the things to consider are your waistline and desired inseam length.  Also, the size of your thighs will be important when considering some of the more tight fitting swimwear available on the market.