Time to live up to my past promise on an extensive overview of tools for watercolor painting. If I had to rank the priority of each, I would break it out as follows:
1. Paper - quality 140lb or 300lb watercolor paper
2. Paints - Artist grades will certainly improve your painting skills and techniques
3. Brushes - This comes in last place because different artists' prefer different types of brushes
Watercolor Paper for Painting
This is crucial. You can't paint on a scrap of looseleaf paper or non-absorbent material that will give you a difficult time to work with. Quality cotton paper lays the foundation for watercolor painting and they come in three types of textures: hot pressed (smooth texture), cold pressed (medium tooth/texture), rough (exactly as it sounds, a bit coarser).
The type of paper you prefer depends on your painting style or what you want to accomplish.
Then the type of paper also comes in different forms such as watercolor blocks, watercolor pads or loose sheets. I generally prefer the first two than the latter. Watercolor blocks are usually sheets of paper glued together on all four sides to form a block. There's a small opening at the top so you can separate the paper when you finish painting. My favorite brand is the Hot Pressed Arches watercolor blocks in 140lbs.
There are other brands worth noting too such as Fabriano which I never had the chance to test but heard that quality is on par with Arches.
Hot Pressed Watercolor Paper
Paper texture is generally up to preference of the artist or based on the types of painting the artist creates. Smooth hot pressed paper is perfect (for me) for brighter colors without the grain. I don't like visible grain in my work so that is why I prefer the Hot Pressed texture than the other two. This type of paper is usually better for wet-on-wet techniques or any painting that requires a bit more flow.
Cold Pressed Watercolor Paper
Cold pressed is not bad and does come in handy when you're painting seascapes, landscapes or anything that requires a bit more grain. Sometimes I use cold pressed watercolor pads for looser works or when I need more control over the flow of my paints. The slightly heavier tooth in cold pressed allows for paint to settle vs. paint flowing everywhere on hot pressed paper.Cold pressed is usually the middle-ground between hot and rough so most artists prefer this type of paper
Rough Watercolor Paper
This type of paper is exactly as it sounds..rough. The tooth on this paper is extremely grainy and visible. This is great for someone who paints earthy paintings or want a super controlled painting where paint settles quickly instead of flowing. The grain on this paper allows paint to seep in without moving around too much. This is the type of paper I least prefer for my own paintings.