how to teach my son to learn new words

A child at that age will learn by playing. Make no sense to put him to "study" or learn to write. Read stories, go out in the park to watch nature, play games with him.

 

first of all put restriction on TV time...let him do anything if he doesnt want to study...but dont let him watch TV for long....when his TV will reduced automatically his interest will become more in studies as he has free time ...
forcing kids for study doesnt produce any result if they dont want to study at all....there are cards games available for teaching small things to kids ...like addition , subtraction, new words etc....buy those...
read books to him...this is a nice way to learn new words....
download activity sheets from internet regarding word learning.....give him those daily ...may be one only...
dont try to overdo or force anything on him....he will learn well only when he wants to learn...