Something that I've learned (through much trial and error) is that one of the easiest ways to ruin a watercolor painting is to overwork it. If you've ever tried this medium, I'm sure you know what I mean. Maybe trying to finish a piece too quickly in one sitting, or by bringing in too many colors and not letting the previous colors dry, over-mixing, MUD. Yep, been there! So here's a little trick I often tell my students to make sure that doesn't happen... multitask!
I often have 3-5 projects on my desk (or desks) at the same time so that I can jump between them. This allows the layers of paint to dry completely before adding another. With watercolor being a transparent medium, it's all about the layers, and building them up slowly to maintain the integrity of those beautiful colors. So there's my little nugget of art advice for the day...keep on painting!