Older eggs: Strangely, fresher is not better when it comes to egg whites and meringue. The fresher the egg, the thicker the egg whites. Increased viscosity means it's harder to whip them up to a grand final poof. Older, thinner egg whites, however, have less stability and the liquid can separate from the meringue. So, rule of thumb - older eggs will whip up better, but may form beads of liquid due to their decreased stability. The choice is yours.
Cold first: Colder eggs are easier to separate than room-temperature eggs. Keeping the egg whites yolk-free is imperative, so separating them while cold will increase your chances of success.
Room temp second: Let the egg whites reach room temperature after you've separated them - they whip faster. Let them stand out of the fridge for at least 30 minutes.
Clean is key: Every utensil and bowl must be spotless. No water, no grease, nada.
Time for beating: Add ¼ teaspoon of cream of tartar to your eggs as you begin to beat them into a frenzy. When they start to foam, gradually add sugar (around 2 tablespoons per egg white).
Keep on going: It may take a while, but you'll need to continue until the egg whites have reached a stage called "stiff peaks," where the tips of the eggs will remain straight up after you've removed the beaters. If you prefer a softer meringue, stop when the mixture has reached the "soft peak" stage - where the tips of the egg whites curl over when the beaters have been lifted.
Put it on your pie: Spread the meringue to the edges of the crust, and try to even the mixture over your pie filling. Bake for 8-12 minutes in a 350 degree oven, until the tips become golden brown.