In fact, it is the same in both cases. What is absolutely necessary to become a good painter is to draw a lot. This may seem obvious, but it is the most important point.
If you are not good at drawing, or if you do not enjoy arts and crafts at school, you may think that you are not good at drawing, so you do not draw much. It is no wonder that they are not good at drawing. If you really want to be good at drawing, you need to draw more and more. And when you start to enjoy drawing, you will surely get better at it. In any case, you must not give up.
When practicing drawing, start by imitating other people's drawings. It is a good idea to imitate the main character in your favorite cartoon and draw many, many pictures of him or her. Eventually, you will get better and better at imitating. Once you are able to imitate well, try drawing in different poses. Try drawing a variety of poses of your own design.
If you keep practicing in this way, you will surely get better at drawing. Good luck!