There are three keys to a long-lasting automatic transmission. First, don't exceed the physical limits with too much power or too heavy a load. Next, keep it cool. An everyday 150 degrees (F) or less (cooler line "out" temperature) is ideal, and under 225 degrees is a good upper target for sustained hard work. Both of these are pretty hard to attain, but under 200 everyday is acceptable, and about 250 degrees should be the absolute sustained limit. Short spurts higher aren't a big deal, but every minute over about 200 degrees is shortening the life of the fluid by oxidation. Finally comes filtration, and a good primer on that is right here.