For building the chest, incline the adjustable bench only to about 30 degrees. That's normally the lowest setting possible on commercial gyms.
A lower incline is even better. If your bench doesn't get much lower, simply place a weight plate under one end of a flat bench. This is much better for the shoulders and allows the "upper" pecs to do most of the work.
Bring the dumbbells close together at the top without touching them. Never clang them together like a dork.
related posts
The scale is just one tool for evaluating your progress, and not even a good one. Here's what you need to know.
This exercise makes it impossible to cheat, and it'll hit your glutes and hams too. Take a look.
If you can't pass this test, then your grip is not only weak sauce, your elbows will start to give you problems too.
The idea of muscle confusion is largely misunderstood. You really don't need to keep the body guessing. Here's why, plus a better way to get strong.