Glazing: dip both sides into glaze move around to ensure all surfaces are completely covered. Lift and let drain, then remove excess by tapping onto the next donut to be glazed or the sides of the bowl. Set on a rack to drip and dry. Ideally very little glaze will drip from the rack if it has been well tapped off in the bowl.
Dipping: Plunge the donut half way up its sides into the icing. Move in circles to help icing move into the donut hole (if applicable). Use a rotating, twisting motion to lift the donut from the glaze while encouraging the icing to stick to the donut. Turn icing side up and set on a tray. The icing will settle into a smooth top. If the icing is the right consistency and there is not excess, it will not drip down the sides, but will form a solid rim.
Filling: Put the filling in a pastry bag with a bismark tip. Insert the tip into the side of the donut, reach nearly to the other side. Squeeze on the pastry bag while gradually retracting the tip from the donut. This makes room for the filling to exit into the donut. Withdraw more slowly as the tip is in the middle of the donut, to allow more filling there. The hand holding the donut will feel the donut filling up, and will have a sense of when enough is enough from the weight and expansion of the donut.
Filling and icing suggestions: