I don’t treat my chicken yard because I have plants growing in there and a deep litter system that I don’t want to mess with but I do preventatively treat my whole coop twice a year. I personally use elector psp for this, the stuff lasts forever. It’s expensive for the bottle but it’s a concentrate that you add to water (there’s dosages for northern fowl mites, red mites, etc online). I spray all the walls, windows, floor, nesting boxes, roosts, and every crevice in the coop.
There’s not much you can do to the run/yard to prevent mites and lice since lice doesn’t live off of birds and mites live in the coop. Keeping wild birds away from your flock is a good preventative because they can transfer those parasites to your chickens. Make sure they have a nice, dry dust bathing area year round to keep themselves free of pests. I have a wood stove and put some wood ash in their spots as a lice preventative as well. Some people say no to wood ash, but I have never had an issue.