It's a good idea to balance the plane laterally. With the high wing trainers it's not AS important. You can hang the tail of the plane from a loop of string, and hold one blade of the prop with your hand. If the plane wants to roll to one side continuously, then add some weight to the wingtip of the other side. You can do it upside down with the string just in front of the stab if the plane has a flat bottom fuse.