make sure no pets are around...since as i know its the biggest problem.
also keep your grow room completely closed...i open my room once or twice a day to check...well i also have some windows with a protective nets....so use that to check on my plant most of the time.
only once in about 12 grows i had spidermites and that was cause i kept my clones at my gf house and she had a cat
good luck!