Keep the belts tight enough with the eccentrics, but not too tight. I generally ran mine tight and when they got loose I just replaced them. I always slap on a new set of belts for the mains. Save the good used ones for practice and quailfiers.
It also gives you plenty of practice swapping belts..... 30 minutes to swap both F & R belts is good
Keep your pulleys clean. I use a mechanical pencil to clean between the teeth. The graphite gives a little lubrication as well and minimizes future buildup between the teeth.
Kevlar belts will "chip" teeth off and the rubber belts survive impacts a tad better, but they shred suddenly with prolonged use. I tend to use kevlar and inspect between every run. A small "chip" on one tooth in the front will get worse very quickly. A small chip in the rear will survive a bit longer.