I love this topic!
First off, the first line in the attached document above is absolutely correct, "unless you are diligent and work hard, the problem will not go away, your crop is doomed and one by one they will fail and die."
Pretty powerful stuff and absolutely true. After months and months of mites I FINALLY don't have spider mites, or at least any to speak of. That's the issue, I don't have spider mites now because I operate my garden as though I always have spider mites. I spray once a week on all plants until they are 2 weeks into flowering with GreenClean. I was always in the camp that organic pesticides didn't work on mites until I found GreenClean, the stuff smells like fancy holiday soap, quite pleasant really, and works like gang busters. I used to use MightyWash, and it worked okay, but you could see how hard on the plants it was. I used MightyWash in an emergency situation late in flowering one time and the plant was dead within a couple of days.
Mite control requires constant maintenance. Even though I can't see any, I have to assume there are at least a couple of those little buggers cruising around just about everywhere, including my garden, looking for a place to start a new colony. So a vacuum 3 times a week, spray once a week, and try my best to keep my grow area a lab like environment.
It's like looking for a job, the best time to do it is when you already have a job. The best time to deal with mites is BEFORE you get them. Don't be lazy. If you see something, deal with it immediately. Stick to your routine. Don't get complacent if you don't see any mites.