My sis did a great job on it. She separated my hair in half (top to bottom) and then separated those sections again (left to right). She inserted hair bands where I wanted the ombre to stop, and then separated the portions in thirds that were to be dyed. Working from the bottom to the top, she applied the dye and let it sit about twenty minutes and washed it out.
I love how it came out. It's something subtle, which was what I wanted.
My sister did a lot of research for the process, and here are some tutorials that were helpful:
Even though I did not dye my whole head red, it gave good tips on dying the dark hair read without bleaching it. I did not have to do it twice, though, since my hair had never been dyed before and the dark color lifted easier than hers.
I first found this video on Pinterest after seeing her after pictures and adoring them. I used the same brand (L'Oreal HiColor) as she did for my ombre.