opinions vary on this subject and I am sure that some of the "know it alls" in the forum will give you their professional opinion.
You will get a lot of advise, some right, some wrong, but take your replies to this thread and see what the most common answer is and use that advise to your advantage.
I am no professional, nor do I claim to know it all, But here is what I do, right or wrong in others opinions: I personally am always changing positions, I ride in the drops when drafting, descending or when I need to be in an aerodynamic position, like when working on a better average speed or sprints.
I stay on the hoods most of the time because its whats comfortable to me, I also am contiuosly changing my hand positions more for comfort.
All the advise I can give is: just ride, get some technique on when to ride in the drops or when to ride on the hoods, find whats comfortable to you, we all have our own and different riding styles, including you.
Good luck and ride safe