Brushing is pretty easy.
Im starting to learn brushing.It just takes time.
Basic thing to look out for when brushing:
1.Dont make the paint look flat(EX. Silver Car:Use different shades of silver to make it look more realistic.
2.Lasso Little parts to brush first.
3.Try to get used to your surrounding when brushing ,like if there if for ex. Bushes , lasso the bush and then place it on the car and lower the transparency
4.Be sure to start off with non-colors(Blacks/Whites)
5.When you get the hang of brushing start doing colors(Red,Orange,Green etc.)
Thats basicly all the things you need to know about brushing.
If you have any questions pm me