The practice of not cleaning until accuracy begins to deteriorate is common, both with air guns and rimfire. In fact, I tend to do it myself. But, you asked about a cleaning regimen for "the best groups". I used to shoot rimfire benchrest, and have done a lot of air rifle tinkering in recent years. I am convinced that, with very rare exception, an air rifle shoots better with a clean barrel. Not necessarily squeaky clean, but clean, same with rimfire. We have all heard stories of air rifles losing their accuracy after cleaning, and taking many rounds to regain it. I can't say that is never true, but I've messed with a lot of air rifles and rimfire rifles, and two things have been consistently true in my experience. First, they shoot better clean, and two, I've never had a barrel that took more than a few shots to regain its accuracy after cleaning. With air rifles, we don't have the powder, primer, and lube contributing to the fouling, so cleaning is generally needed less often, is easier to achieve, and seasoning it after cleaning is quicker, all assuming a good barrel. Your experience will determine what is right for you, so take my comments as worth what you're paying.