You want to take your adjustable bench over to the cable crossovers and set it up in the middle. Set your cable handles to the lowest setting. Make sure your elevation on your bench is at a comfortable height. Keep in mind, if your bench is too high, you'll be working your shoulders and if it is too low, you'll be working your middle chest. This is an upper chest movement.
You want to start with a very light weight. Due to the movement and stress of this motion, it doesn't take a lot of weight to be effective. Grab both handles, lean back on the bench, get your feet square, and steady your head forward. Keep your arms straight, only allowing a slight bend in your elbow. Rep range should be 15+.
For safety reasons, when your last sets are getting a little too hard, keep in mind placing the weights back down and not just relaxing your chest and arms. Not only will slamming the weights break equipment, but you run the risk of pulling your front deltoid in this position. So, be sure to control the weight and not let it yank your shoulder out of place. Don't be the accident prone guy in the gym.
Go forward and get those gainz.