Hello Vejita! Faces are mostly difficult because they concentrate a lot of detail in just a tiny space, and also because they almost always became the focal point of the mini, so if there is an error there it will be spotted almost instantly. Keep painting and it will be less of a mess ;)
Warpaint on the skin looks ace though!
Two things that you could do to improve your paint control are:
First, try to dilute your paint just a tiny bit more, you are almost there, thickness became noticeable specially on the upper areas of the skin. Also you'll need to play with this as not always paint ned to be diluted to the same grade.
Second, and almost more important, wipe the excess paint from your brush before touching the miniature, you will see that doing this will do your brush a better point and doing that will help you avoid paint lumps and brush strokes on the miniature.
Have fun painting!! ;)