As was pointed out earlier trim is secret to holding a constant altitude. But before you trim the aircraft has to be in equalibrium, that is not climbing or descending (level flight attitude) and at the right airspeed (correct power setting). I find many new pilots rush the trim and never really get the airplane properly trimmed so they end up chasing the altitude because the aircraft will climb or descend as soon as the pilot becomes occupied with any other flying duty. With respect to Molesworth 1's comment about holding altitude not beeing important....I could not disagree more. Holding altitude is like every other flying skill, you get better with practice. If you make an effort to fly accurate altitudes you will quickly find it becomes easier and easier.