The OS LA series are a very user-friendly engine. Keep in mind they are a plain bearing engine rather than a ball bearing example. You not only need to break in the piston/cylinder liner but the crankshaft/bushing as well as the conrod lower and upper ends.

Best way to do that is run it per manufacturer's instructions. Most important factor is to use a proper fuel. I wouldn't recommend an all-synthetic blend for the first gallon. At least some castor and a minimum oil content of 18-20%. Go to a smallish prop and run it to just barely below peak RPM. A couple of tankfuls like this on the ground will give you an engine capable of maximum performance and longevity.