My college watercolor instructor was asked how she would rank the importance of watercolor supplies when out purchasing at the art stores. We were all starving art students after all and wanted to know where we should focus our limited spending power. Paper came first, then paint, and finally, brushes.
The type and quality of paper you use can dramatically affect your paintings. A good exercise is to paint the exact same object on different surfaces to see how the paper influences the final image. In this particular class, we were asked to paint a white object on various types of papers, translating the lights and darks we saw on the object into a monochromatic color palette. I chose a sugar bowl and my favorite color ever: quinacridone magenta with the addition of Payne's grey for shadows.
For the ultimate in texture, try rough paper. Paint tends to settle out on rough paper, creating a grainy effect. Dry brush techniques are easy-peasy on rough paper as the brush can glide over the surface without getting into all the nooks and crannies. This paper is not good for detail work but instead, is great for a more impressionistic look.
Also called "not" paper, this paper has a medium-textured surface and is probably the most popular choice for watercolorists. With cold press paper, there is a nice balance between the texture effects one can achieve as well as detail work. This paper handles dry brush techniques in a subtle way and can handle a good deal of scrubbing and scraping.
While wet, hot press paper is made with the addition of heat and pressure to make a smooth, texture-free surface. Because there are no valleys in the paper for the paint to travel into, paint tends to slide around unpredictably on hot press paper and dry in hard lines. This paper is excellent for pen & ink illustration work as well and is probably the go-to choice for art journalists.
This stuff is not really paper at all but instead a sheet of plastic. (The company that makes it calls it "synthetic paper.") Because there is zero absorbency, paint just slides around like a wild animal and each stroke of the brush removes the paint you just laid down. Essentially, with Yupo, you push the paint around until it lands in a pleasing formation. Don't like the results? Simply rinse it off and start again! (Some paints will stain and leave behind ghost color.)
And finally, a note about paper weight. All types of watercolor paper come in different weights: the higher the number, the thicker the paper. Get the heaviest paper you can afford (140 lb is a great place to start.) Watercolor is tricky enough without having to deal with buckling and warping as well.