How should I break in my 250r suzuki quadracer engine after rebuild?

when my banshee motor got rebuilt last year my mechanic told me the way to break it in is to ride in 2 or third for a few days and also try to stay at the same rpm. Riding in second going about 20 or 25 mph is good for it when my banshee motor got rebuilt last year my mechanic told me the way to break it in is to ride in 2 or third for a few days dont keep reving and letting off the gas stay at a constant rpm . Riding in second going about 20 or 25 mph is good for it.