If you have trouble transferring your drawing or sketch to your watercolor paper, whether you draw first or simply paint here's a good tip. Fold your drawing in half and then in half again, in both directions, horizontally and vertically. If your drawing does not go all the way to the edge of the page, make sure your second fold in each direction lines up with the edge of the sketch and not the edge of the paper. If you don't want to fold up your sketch, make a photocopy of the sketch and fold that. When you unfold it, you now have a grid.
Tape your watercolor paper to a board. Now make tic marks on the tape. Use a ruler if you need to. First make a mark at the half way point on each side. I made the half way mark tics longer than the other tics. Then on the tape only, mark your corners and then make a tic half the distance from the corner to the half way mark. Don't draw a grid on your paper, instead visualize it using the tic marks on the tape.
Now sketch out your drawing lightly in pencil using the the folded grid and the tic mark grid as a guide. Or paint without drawing first, yet still using the grid method as a guide.
Good luck, have fun and enjoy painting!