Look through various art galleries and find art that you like...then try to duplicate it for yourself.

As you look at what you did and compare it to the original, you will start to see the little nuances that will help you to learn to do better.

This is suggested as a learning lesson, I am not suggestion for your personal art that you simply duplicate other peoples things. But if you use this technique as a learning tool, then when you do your own original art, you will remember what you have learned.