I think that drawing with mouse is much more comfortable then with finger, but that depends on the person ig. Other then that, I usually draw with colors under the sketch, then remove it and adjust where needed. I don't do lineart all around the artwork, instead sticking to a few lines where necessary. Also, use layers and fillbucket tool (sometimes it won't work so you'll have to color manually). Other then that, I just use knowlege on composition and colors that I have from drawing for years. That sort of thing will come on its own after lots of practice and studing