Watercolors are challenging, more so than acrylic or oil, IMO. But , remember to let the water work for you. So, don't paint with tons of brush strokes, as you might in acrylics. Let the paint flow. Use big brushes for big areas, small brushes for small areas.. YOu can mop up excess water with paper towels blotting.
Think what your lightest areas will be first, and leave them blank. You can even use latex resist to protect small areas, like whiskers, that you need to remain white no matter what sort of paint is put down around/over them. Then you remove this resist, the very last step.
Experiment with wetting the paper, then putting paint into this, so -called "wet on wet" technique.
Utilize some drybrush for manes; dry the brush out completely before applhying some fairly dry (not soupy) pigment.
Don't paint ever inch of the canvas, leave some "blank" space.
When you go to the artstore, buy a "Block" of watercolor paper. It is glued on all edges so that it does not warp when you paint. When you are done and the painting is fully dried, you insert a razor knife between the glued sheets and free the one sheet you have just painted.