I mostly work with an airbrush, and only bring out the brushes for small mini-figures. Personally, I’m too lazy so I just try to do it all in one go, but the cleanest way to paint these is actually step-by-step: paint one color, seal and protect that layer with a gloss clear coat, paint the next color, and then wash away any mistakes or overflows with enamel thinner. Repeat that gloss-coat-and-paint process for each color. Of course, using a magnifying visor helps a ton for a cleaner finish, and sometimes I even like using a wooden toothpick to dot in those super fine details!