If you just want to do some sport flying, locating the CG on the wing spar is a good place to start. The spar on most planes, is located at about the 25% of MAC point, which gives a 10% static margin. This results in a good balance of stability and reasonably good aerobatic ability for a novice flyer. If you want to fly more aerobatic maneuvers, you will need a reliable way to adjust the CG location. The factors effecting the plane's stability and aerobatic performance are discussed at my website, www.rcaeronauts.com. Check them out and good luck.