the best way to teach tennis young players is to focus on tracking the ball, hand eye coordination, watching the ball spin, making sure you run to the ball naturally and make clean contact every hit. Once your son perfects these skills, he can focus on more technique to advance his game. focusing too much on technique first will hurt his tracking skills.
for more info, try youtubing the the youtube channel PlayModernTennis. or youtube Oscar wegner.
i know he's only 8 years old, but when he's older, have him read the book The Inner Game of Tennis. it's amazing
I won many high school #1 singles tournaments using this info.
also, i still hit against my basement wall lol