Check out THIS ridiculous hair colour!! And yes, that is me, please ignore the cigar and the fact that I look all evil in that picture. It's the only picture I have of the new colour I made.
That photo has not been adjusted in any way, that's actually the hair colour I have.
I know it's not the colour you're going for, but if anyone has a difficult time keeping up red hair it's me. I only use salon brands, and to be completely honest, there is pretty much nothing you can do to maintain your colour perfectly. You CAN make it last a bit longer though, though it will eventually just get really dull and, depending on what your colour was mixed with, pink (haha as in my case).
I have found two particular shampoo and conditioner sets that make a NOTICEABLE difference. I mean, most of the colour extend shampoos DO do what they claim, just not very well. And if I'm going to dish out the cash, I damn well want it to work. The two best by far I have found are Pureology (which is insanely expensive by the way, if you can afford it go for it, but I surely cannot), and the L'Anza colour care one (don't remember the exact name). The latter is also quite expensive, even more than most salon brands, but cheaper than the Pureology one.
Washing your hair with cold water makes a pretty big difference as well. It closes the hair strand so that colour cannot escape when you wash it. So f you're wetting your hair at all, use only COLD water. Sucks hardcore, I like to be warm and toasty, but I guess it's the price I pay.
I actually mix my own hair dye colours, and I really like when they are vibrant. If they're even starting to get dull, pinkish, or brownish looking, I dye it again. I use Special Effects dye because I can leave it in all night if I want (it's a vegetable dye, so there's no damage at all) and I can make my own colours. However, too keep my hair such a bright colour, I do dye my hair every 2-3 weeks.
So good luck with the hair, in my experience that particular colour doesn't actually fade that quickly. Believe it or not (not sure how THIS works, but yeah...) red is one of the quickest to fade but also one of the most difficult to get completely rid of. So there will always be SOME red in there, and since you apparently don't want to go too red, I don't think fading will be that big of a deal. I think my biggest suggestion would just be to use SOME colour extender shampoo (preferable one of the ones mentioned, but they all work to some degree in my experience and God knows I've tried many), always use COLD water on your hair, and make sure you have a heat guard on your hair if you use any heat tools. Because once again, the heat can open up your hair strand and pull the colour out as you style. My flat iron has turned red on numerous occasions when I forgot that part.
Oooh, and don't wash your hair more than you absolutely need to! I only do mine every second day, and every third day in the winter if I can pull it off (my hair is much drier in the winter). Good luck!