1. Test out your colors.
Have a small sheet of watercolor paper to test your colors before they go down on the painting. This will save you time and frustration during your process. Also, choose a simple color palette when first starting out. This will help you ease into more complex color combinations later on.
2. Use simple reference photos.
I like to use reference photos for shadows, highlights, and feature placement. I also use ref photos for cool hair styles and skin tones. If you create from your imagination a reference photo can help add a realistic aspect to your artwork. I heard about unsplash.com from Ivy Newport over on Facebook.
3. Dont' rush - take your time.
Sometimes, I like to set a timer while I'm painting to help set my creative juices in gear. When you are trying to improve on your watercolor, take your time. Think about what you are putting down and why. Over time you will get quicker and quicker.
4. Upgrade your art supplies.
I had a super simple watercolor palette for the longest. Once I got serious about watercolors I invested in brushes and started upgrading my paint. You can just start with the primary color tube paints and a few good brushes. You will see the change in quality when you switch over.