Step 1: Wash/wet your hair as sparingly as possible. I personally wait from 6-10 days if I can.
Step 2: Wash/wet your hair in as cold of water as you can stand. The cold keeps the cuticle closed.
Step 3: Only use sulfate free, color safe shampoos.
Step 4: Use as little heat as possible. Higher temperatures can darken bright blondes or fade out richer colors. I've seen straighteners annihilate silver hair in one swipe.
Step 5: If you have a solid color, a tinted shampoo/conditioner might be a great option. Always consult with your hairdresser before you buy one online. They might be able to mix you a custom one (I can!). Some tinted shampoos sold online have shades that are very hard to remove (cough overtone cough), so be careful.
Step 6: Stay out of chlorine, salt water, and well water. If you live somewhere with only well water, I highly recommend this water filter. I promise you can install it yourself after studying up on Youtube.