Wet on Wet: This technique is achieved by wetting the paper first with a wash of water then using watercolors on top. It is great for painting landscapes, skies, or soft flowy scenes.
Wet-on-Dry: This technique is used for precise and defined shapes. It is achieved by applying watercolor on dry paper.
Building Color: This happens when you let your first wash of color dry and then add another layer on top of the areas that you want to make more vibrant or darker. This is achieved by using different values of the same color.
Gradients: This is very similar to the previous technique. However, it is mostly used to slowly transition from one color to the other. It could be very useful for painting the sky during sunset.
Tip: When creating gradients, make sure to use colors that are close on the color wheel, and go well together. This is to make it look harmonious and to avoid muddy colors.