Marilyn-Wet on wet- You really have to use thick watercolourpaper, tube paint is slightly thicker, which i prefer, Wet the paper with a spongefor a large area say you were doing a small area check that a shine has then appeared and with a  fully loaded brush with the paint not too thin ,then just put the tip  of the brush into the wetness. The paint will float across on its own. Look  at the tube and it will tell you about whether its granulated colour which are good for wet in wet, all tubes and pigments have their different ways of performance.Ultramarine  is a good one for granulation, as an example. Keep your water clean , change after each colour you use.

Sue- Look out for these if you are in France- Louve  Paints- I had some given to me they are in tubesand are excellent bright colours with good granulation . I have looked on e-bay but havent seen any here. . The ulramarine beats any ive used for granulation !