Before I get into how I paint, let me tell you what I use. I have for some time really enjoyed Windsor Newton watercolors. I use mainly Cotman, but have several Artists' Water Colors. I also use Grumbacher every now and then, but not often. I prefer tubed paint, I feel like I have more control this way.
The colors you'll find in every painting of mine are:
Dioxazine Violet (Artists' Water Color by Winsor Newton)
Alizarian Crimson Hue
Rose Doré (Artists' Water Color by Winsor Newton)
Hooker's Green Dark
Not 100% sure of the size for the blue one, but I believe it's a 2 or 3 round by Winsor Newton, and the red one is a 3/0 round by Princeton. I suggest having a wide range of sizes, you never know what you'll need. The largest I own is a 12 round. I choose round because I find it easier to blend and the brush holds more water...in my opinion.
Which leads me to my final thought before we go into painting. It's more of a disclaimer. This is my way of painting. I am self taught in watercolors and I highly encourage learning all techniques possible before deciding what works best for you. As a teacher myself, it's important to try everything, especially in watercolor. It has so many possibilities, and you probably won't learn them all by one teacher.
I use a lot of water, a constant back and forth from the water, to the paint, to the water, to the paper, and repeated. Always start with really watered down color, you can always add paint, but rarely subtract it.
You don't need to have complete control of the medium here, the more loose you are the better!
I have found keeping all of my paints, brushes, water, and paper towel on the side I write with to be very helpful! Remember, water, water, water!
Tip: If you have too much water in a small area, dry your brush and return to the wet area. Your brush will soak up any excess paint you don't want. This is also very helpful in blending. Remember, your brush is meant to hold water like a sponge.
After I decide where my light source is coming from I begin using my 3/0 brush. I use Rose Doré for the base of all my skin tones no matter what color they are in the end. The reason is because red works in highlights and in shadows, it's a great undertone in my opinion.
With water mixed in with my paint I begin using the Rose Doré to layout where my shadows are. I personally enjoy "maps" when I paint, because I rarely do color studies.
Tip: Apply the paint where it would be darkest. Look at eye closest to us, above the cheek, that's where I laid down my red. Take your brush to the water, rinse it, lightly dab onto the paper towel, go back to the painting where you laid your red, and pull it. Dry your brush and go back and pull again. Now you're blending!
Find a rhythm to how you paint, you're working with an element of the earth, not a machine. Always keep that in mind as you paint. The best way I learned how to paint was first allowing the watercolor to do what it wanted, then figured out how I can control what it already naturally wants to do. If you go into trying to control the medium, it will most likely make you leave your painting or worse yet, throw it away and never return to using watercolors.
Next step: getting rid of the white remaining!