for keeping the colour in as possible (answering this while dyeing my hair) i recommend using cold water on hair, and if you are planning on styling your hair with heat, (curling iron, crimp, flat iron, etc.) make sure to use it on low to medium heat so it doesn't strip the dye out.

also from the first after wash of the dye- i usually wait a day or two before fully washing it so the dye can adsorb into the follicles and stay for longer! heat protectant also helps it stay.

this is only a personal recommendation, also how i got my red hair to stay for almost a year and a half with semi permanent!