GREAT BOOK!
The Proficient Pilot
Barry Schiff
AOPA 1980
This book will help you understand things about WHY your model does what it does. It explains things in "layman's terms" making some of the more difficult parts of the theory of flight understandable.
It is aimed at the sport/private pilots of full scale aircraft, but EVERYTHING works for the average 4-channel model aircraft.
Why you can get a longer glide at a faster airspeed. Why you can keep the plane n the air longer dead stick at a glide speed slower than that maximum distance speed.
Why the airplane requres a certan turning radius at some given airspeed and a larger radius with a higher airspeed.
All sorts of things that will improve your understanding of how the model works... and that can't do anything execpt help you to be a better pilot.