How to dye my hair professionally?

I would like to learn how to dye my hair using hair dye that I have to mix on my own, (like the kinds that professionals buy at Sally's Beauty Supply for their salons). What tips and information do I need in order to dye my hair properly?? What brand should I choose? I've always used the boxed hair dye from Wal-Mart or the grocery/convenient store and they always seem to have an orange, gold, copper or purple hue to them making my hair look cheap. I would rather my hair look more natural than that. My natural hair color is medium to dark brown and I would like to stay in that range. Also I should probably stick with a cool color since I have pale skin with some red undertones, so any warm colors like orange, copper, red or gold and other warm tones tend to make my face look very red and blotchy or pinkish. So I think I need a cool color since cool colors don't bring out the pink in my skin. Thanks for the help!