I don't use it myself, but other people use neem oil as a preventative.
I've fought mites with habanero and nicotine tea sprays.. rosemary. Once they start spinning webs I'd say start over.
Habanero is a bitch to work with and is pretty good.. Gotta cycle it with other natural stuff with a lot of applications so it takes time..
Rosemary is excellent at killing quickly, but I've also damaged the plants with it so you have to be careful. Smells great, too!
Now I use nothing but live ladybugs. If you can manage just to keep 3 or 4 hanging out long term.. you'll never worry about mites again. Hate The Borg!