When applying brown hair color go for your target shade and apply it to the roots. When it comes to the ends of the hair for the first time it might be wise to do a shade lighter than your target. This way your hair feels shiny and rich, but not too dark on the ends. The color will blend just fine if it's only one shade different. When it's time to touch up your roots, you should apply the color to the roots and let it sit there for the manufacturer's selected time.
Normally around 30 minutes, leaving the ends free without any color. Right before the color is ready to finish, add some water to the ends and to the leftover color in the bottle. Give it a little shake and apply it to the ends only for a minute or two. Since the ends are already color-treated, they don't take as much time as the roots. By leaving the color on too long from the roots to the ends that could give the ends an inky look, which is unwanted and unnatural. Those are just some of the things to think about, when dying your hair brown.