There’s an enormous amount of information available to help the beginning watercolorist. Rather than rewriting the internet, here’s a few resources that have been especially helpful on my journey.
WetCanvas.com: Hands down the best and most helpful forum for artists of all skill levels. It’s vast, covering many techniques, topics and media. This link goes directly to the Watercolor Learning Zone. I have had the privilege of participating since 2010; many posts here were originally published on WetCanvas. There is no skill level too amateur, nor any question too basic, to be welcome there.
Jane Blundell Art: Jane’s website features an extensive array of resources for watercolorists in addition to her lovely portfolio and sketchbooks. Check out her work for inspiration, and her Tutorials and Resources pages for information on techniques, color, palettes, and much more. She also has an extensive collection of swatches, and you can buy her books of mixing charts too.
Handprint.com: Bruce McEvoy has compiled one of the most exhaustively detailed resources for watercolor paint and materials available anywhere. His pigment database remains an invaluable resource for understanding, comparing, and choosing paint. If you want to know everything there is to know about watercolor techniques and materials, and the science and history behind the art, this is a great place to start. Brew some coffee, and prepare to get lost.