As far as my brushing on technique, I just mix a smaller batch of Rit, and using a paintbrush to apply it. If the design has a lot of black lines seperating the ares i want covered, I paint as close to the black line as I can. Trying not to cross over the line into the area that I want a diff color. sometimes hard to do, so some cross bleeding may occur.
If I am brushing on two different colors, not seperated by a black line, I brush on the darkest color first. when i dye the lighter color next to it, I still paint carefully as close as i can to the darker color, trying not to cross into the area.
I have no exact water to Rit ratio, but basically the thicker the mixture, the easier it is to control it and keep it within the lines.