The stock answer to this is that you can't get rid of fat from a specific area. This  is repeated frequently and emphatically by almost everyone involved in fitness. Given that it's the go-to answer, you would think that there's a pile of evidence to support it. In fact, the evidence is surprisingly weak. On the other hand, there's no evidence that you can exercise to burn fat from a specific area either.
What we do know for sure is that our bodies have preferred places to store fat - and the abdominal area is one of them. So you're not likely to have a fat-free belly until you're a healthy weight. The best way to be a healthy weight is of course to have a healthy diet and to exercise regularly. Any exercise helps with weight control.
Even if it doesn't burn belly fat, regular ab exercise will make a difference though. The deep core muscles pull the abdominal area flat and having a strong core can make a real difference. In fact it's often the case that what people think is fat is just poor muscle tone allowing the abdomen to protrude.
So, the best things you can do to look slimmer around your middle are to make sure you're a healthy weight and do some core training.