How I prepare for hair color

I have dyed my hair at home for years. I easily get bored with my color and feel a need to change it up, but I don't have the moolah to go get it done at the salon! One thing I have learned over the years is that if you color regularly, you need to prepare your hair for even color absorption. Virgin hair can also benefit, but most likely will take more evenly than regularly colored hair.
At least one day before I plan to color, and preferably longer, I do the following steps to prepare my hair for coloring.
The first thing I do is clarify my hair with sulfate shampoo that contains EDTA and/or citric acid. This removes all manner of build up, including stylers, mineral deposits, and also (this important) lifts some of the left over color from your previous coloring. The reason that's important is because you need to make room for the strands to accept NEW color.
After clarifying, I do a protein treatment. Protein fills in any holes (porosity) in the hair shaft. This also helps the color absorb evenly. I use this recipe for Science-y Hair Blog's gelatin protein treatment. I love this PT because it's cheap, easy, customizable, and it WORKS. Of course, if you aren't the mad scientist type who enjoys cooking up hair concoctions in your kitchen, there are many store bought options. Some options from Sally Beauty Supply are Ion Effective care (mild protein conditioner), Ion Re-constructor (protein treatment conditioner), aPhogee 2-step (strong protein treatment, comparable to the gelatin PT), Joico K-Pak. There are also botique type treatments available online from Spiral Solutions, Curl Junkie, and Jessie Curl (maybe more, I'm not sure..).
I follow this with a moisturizing deep treatment. I prefer to play mad scientist again and mix up my own DT with Generic Value Products (Sally's knock off brand) Conditioning Balm with some honey and coconut oil. I leave that in for at least 20 minutes with 10 minutes of heat, 10 minutes of cool down time. Sometimes longer if I just don't feel like washing it out. I have left DT's in over night, but I let my hair down to DRY because leaving it wet leaves it in a stretched state and prone to breakage.

Don't color the day you wash. Your natural oils will protect your scalp from irritation, so it's best to color on day old (or longer, I have insanely dry skin, so it takes my scalp at least 2 days to build up enough oil to properly protect my scalp).

It's so much easier to spend a couple of hours preparing for your color, than it is to try and fix uneven color once you dye your hair! In some cases, you can't fix it at home and will have to shell out the dough to go to a salon so a pro can fix it.
One last thing, at home coloring works best if you stick within 2 shades of your natural color. This is particularly true if you're going lighter. Darker is less tricky than lighter! So unless you are experienced in going lighter, please don't try to go platinum on your own.