How to dye natural virgin hair.?

I am contemplating dying my hair red, though i don't want to do it wrong and end up with my roots being lighter than my ends. So i was just wondering do you go from root to end or end to roots. Plus my hair is virgin and very thick, so do i keep the color in a little longer than the directions on the box says. I'm thinking about using the L'Oreal high color line.

and im definitely not talking about crayola red Ronald McDonald red hair