[Nyororin]

The hard way;
You spread the hair out thinly on plastic wrap or foil, and spread dye *paste* (not liquid, because it runs!) over the sections you want to dye. Then put another sheet of plastic wrap over the top and roll them together - you want to make sure that the hair is always very thin between the two sheets. You can also put wax on the parts you do not want dyed to be safe and keep the line straight.
You need to keep the hair horizontal as the dye takes to avoid running, so it`s best to stay lying down with the hair stretched out.

The easy way;
Use clip on hair.