There are many methods that make good matzo balls, and also many opinions about just how light or heavy a matzo ball should be. But one thing applies to any recipe you use: don't over-handle the mixture when forming the balls. Doing so makes them dense and chewy—and not in a good way!
Use just your fingertips, work the mixture as little as possible, and don't worry about making perfect smooth balls: the surface texture evens out as they cook.
Recipe: Matzo Ball Soup