Now that you've got a great bike fit and have been working on strengthening your core, it is time for the final key to good form on the bike; stay relaxed.
To do this when you're riding, make sure you keep your elbows bent your hands properly positioned. On a modern bike the most comfortable place for your hands are on the brake lever hoods. You can vary this up a little bit by bending your elbows tucking down and getting a little bit more aero.
There are some other spots that are comfortable too. From the brake lever hood, you can move your hands backwards to the handlebar. Now sit up and breathe a little bit.
When you are climbing, place your hands on the bar tops open your chest for deep rhythmic breathing. If you are going fast or descending, it's best to get in the drops where you can decrease your wind resistance and have the most control and the lowest center of gravity.
Use these hand positions to ensure your good form on the bike!