Lower your body fat. For most guys, your gut is the first place your body stores fat.
Do more cardio, do it regularly. Cut back on your
calorie intake a little (not too much or you can cause your metabolism to slow down). Cut down on soda, beer, dessert, bread, etc. Try to split your meals into five or six small ones instead of two or three big ones. Don't
skip breakfast.
Weigh yourself every morning. Get an electronic body fat meter and check that every morning -- they're not very accurate, but good enough for comparing readings from day to day to see if your % body fat has changed.
It'll take two or three months before you start to see a noticable difference.