I leaned watercolor painting from YouTube, if you are struggle with watercolor??! no problem I can give some tips that I learned by my mistakes.
You should know how to sketch properly, but you don't need to do detailed sketch.
Another important thing is shading, you must be good at shading
Lights and shadows
You must have the ability to understand where the light coming from, (actually it's a very simple thing, anyone could do that)Color Values is the another important thing, if you choose wrong color values your painting will be very differed from your reference.
Below I mentioned some YouTube channels for beginner artist. Check out and make your works next level.
Vinita Pappas
Michael Solovyev
Paint with David
Maria Raczynska
Jagadeesh Narayanan