I had identified this as a leak in my game a while back and took steps to correct this.
1) A lot of online players will float the flop with any two, especially over cards, and look for you to check the turn to bet big to push you off your hand. Easiest way to combat that is to look at your position, the texture of the board and bet the turn around the same percentage as your flop bet more often. Those that float often fold the turn.
2) You must punish draws - if a draw hits the flop but misses the turn, often if you bet aggressively on the turn the draws will give up, whereas draws will often call the flop as there are more chances to improve. Harder to call if you only have one card left
3) Many people are calling stations and you can extract value by betting the turn and going to the river, especially if you have position on them.
You need to vary your game by mixing it up - betting your draws sometimes, but not all the time. The more you know about your opponent the better.