Basically, you would first have to come up with some form of target. Probably something based on a turret but with no weapons and an insane amount of cutting armor. Otherwise, shooting at anything that isn’t a creature of some sort will never make your skill increase.
Then just make a building in JSON, have it spawn near highways, and have a bunch of target creatures spawn in it. There are a number of mods that add buildings that you can use as a guide.