Using your forwards is the best way to create gaps in your opponents defense. Use them to run at your opponents defenders forcing them to tackle and go to ground. Your players will get up at the end of your turn, your opponents will only get up at the end of his and that effectively means that he will have fewer players to use in his turn!
The Forwards also have the added advantage of being able to ruck. Rucks are a great way to secure the ball, suck in the defense and set up an off-side line... 3 great ways to ensure your team can keep going forward.