hold the plane by the wings, nose toward your belly, palms up, thumbs wrapped over the leading edge, one hand on each side of the fuselage. Your finger tips should be right under the main spar. raise the model up on your finger tips. If you need to shift your fingers forward to make it balance, it is nose heavy, or to the rear, it's tail heavy. Shift your radio gear around (best) or add ballast (not so good) until your fingers are right at the balance point when you do this.

Most models will fly well if they balance on the main spar, or 1/3 of the way back from the leading edge of the wing.