One of the most important things when learning to paint with watercolor or improving your watercolors is the use of quality paint. If you're not using quality artist grade paints, you may not get the range in value in your painting. You also may not be able to get nice rich dark colors. Artist grade paints will have more pigment and less filler. Student grade paints will have more fillers and they may not have as good a quality of pigment in them. Student grade paint should be left to students of high school age or earlier. If you really want to learn to paint watercolors, start with artist grade paints.
My current favorite paint is Maimeri Blu Watercolors. I teach watercolor painting classes for beginner and advanced adult students. The colors I recommend for my classes are pictured in #1 of the photo shown, there are 10 colors total. I prefer to squeeze the tubes of color into a Tom Lynch palette and I allow them to dry before I use them. This method saves on paint and is more economical than using the paint fresh from the tube. Photo #2 shows my class palette, plus 3 extra colors. Photo #3 are my Zoltan Szabo palettes, I had taken a bunch of his workshops, which I absolutely loved. The two palettes on the right in that photo show the colors he recommended in his workshop and the one palette on the left is my test palette for new colors. These are great palettes for traveling. Photo #4 is my small travel Hommee palette, great for taking along on an adventure or a hike. Photo #5 is my very first palette and it is filled with Winsor Newton paints and more earth tone colors. When I first started to paint with John Alderdice, he recommended the colors shown and the Winsor Newton Artist paints. He always said to use the best quality available. Which would remind me of my college days and the saying "garbage in, garbage out". Photo #6 shows my scrap palette. I have taken a butcher's tray and placed the colors I have removed from my other palettes around the edge of this tray. I remove colors from time to time from my regular palettes if they get too low or if I decide I would like to switch a color for a new one. No need to waste the paint! Sometimes I will squeeze just a little bit of a new test color onto this palette.
I highly recommend Maimeri Blu watercolor paints, they are Italian. They set up well in a palette and they refresh easily with the swipe of a wet brush. They have excellent lightfastness, so far I haven't had a single MaimeriBlu watercolor painting fadeand I have been using the paint since 1998. The second brand I would recommend are the Winsor Newton Artist Grade watercolor paints from England. You can't go wrong with such a well known brand. However, the Winsor Newton paints set up harder in the palette, I find it best to add a few drops of clean water to the tops of the colors in the palette before painting to get them to soften up a bit. I am testing another brand of paint, I purchased only one tube so far of M. Graham watercolors which are made in the United States and so far, so good ... I really like it. The M. Graham prices are similar to the Maimeri Blu paints and on some of the colors, the price is better.
Artist grade paint gives you rich deep gorgeous colors. If you think it is too expensive, start out with fewer colors. A limited palette of colors is a great way to really learn your palette. Buy the best you can afford, you're worth it!