What should I know before dyeing my hair?

In a couple of days, I’m going to get my hair dyed (for the very first time) at a salon, and I have no idea what the procedures are. If it makes any difference, I’m going dark. . . But I don’t know if I should/n’t wash my hair the night before/morning of. . . If I should get a new shampoo/conditioner. . . (Right now, I’m using Pantene: Moisture Renewal. On the back it says that it’s gentle enough for color-treated hair, but I want to be sure)

Is there anything else I should know, aside from the above?