Make sure that the sugar beaten with the egg whites is completely dissolved. Rub a little of the mixture between two fingers. The undissolved sugar will feel grainy. Cook meringues at the lowest oven temperature.
Beat the egg whites until they form soft peaks, then sprinkle the sugar on top of the egg whites. Allow the egg whites to sit for 5 minutes without stirring. Beat the egg whites and sugar until stiff peaks form. Spread the meringue over pies and bake as usual.
It's a good idea to leave the meringue in the oven with door ajar and heat turned off after it's been cooked. That way, is doesn't have a temp-change-shock. Keep the meringue out of draughts while it cools, too.