While I agree that 25% MAC is a great place to start I will disagree that this is the optimum setting for most airplanes. If you find that the airplane required a fair amount of up trim and/ or lands on the fast side odds are you can safely move the CG back some. Contrary to popular belief a nose heavy airplane is not easier to fly then one that has the CG correctly adjusted. Of course a tail heavy airplane is just miserable and short lived.