Some plans, I believe, maybe most of them, advise what the incidence on the horizontal stabilizer should be. If it is zero (many are) then a level on the stabilizer will give you what you are looking for. If it has incidence, say + 1 degree, simply set the airplane with the horizontal stabilizer at + 1 degree and the plane will be "level" or at its normal flying attitude. This is assuming the plane was built to specs. I believe this to be correct but it may be some of that bad advice we have been discussing.