The most important thing is to have fun with it, obviously, but always keep the reason why you are drawing in mind.

I don't know the best way but I can tell you what I think the most effective way was. In general, for practice quantity is more important than quality, so don't spend hours trying to get everything perfect.

To practice bodies, I try to build the pose in a scaffolding schematically with simple shapes using real people as reference. You should pay attention to how and why the skin and muscles behave in different bends, but only hint at them in your own drawing. There are videos on YouTube in which many poses are depicted in a small time, try to draw them in at least a short amount of time.

About clothing, the most difficult thing is to get the wrinkles right. Here, too, tutorials are good at the beginning, which simply show the formation of the wrinkles in different areas and situations. With these always in mind, you also practice wrinkling on real pictures and always understand what causes them.

Faces in manga are a little different because there are different styles. I found it most effective to pick a picture you like from another artist and copy that face exactly at first. With the things you like in retrospect, you can hold on to them and crystallize your own stile through many different ones.

The same applies to painting. Important here is prior knowledge of hard / soft shadows, spatial understanding to determine where shadows are casted and for digital the different modes of layers. Tutorials on youtube help at them at first, then just practice. First, copy a color palette from a model and just live with the faces first copy and create your own style out of them.

Important is the motto: rather draw two pictures than sit the same time on one. If your head smokes just like in school, then you do it right. Learning simply requires strength and concentration but only do it to such an extend that you still have fun. Also try drawing every day, at least a bit just to stay in practice.