There are a few tips to beating air into egg whites and producing a buoyant foam - none of which involve rocket science.
The first step is that the bowl and beaters should be absolutely clean. If there is a little oil residue in the bowl or a little hint of yolk in the whites, it will interfere seriously with the formation of air bubbles. The bowl should also be dry as water will inhibit the formation of the foam. One of the steps you’re taking is important, beating the whites at room temperature. The proteins in the whites expand better when warm, so you will get better volume from the eggs. Older eggs also whip more easily because of chemical changes that have taken place as they aged.
You’re also right about wanting to add something to the mix. You should start with a pinch of salt in the whites, which will help firm up the proteins. About a quarter-way through the beating process, you add an acid to the foam, which stabilizes it and helps keep the bubbles from bursting when you stop beating. Most people use cream of tartar, but one or two drops of lemon juice or vinegar will work as well. Finally, if your whites seem unstable at the end of the beating, or if you have overbeaten them - and if your whites will be used in a dessert - beat 1 tablespoon of sugar in for only about 15 seconds. This will restabilize the foam, but you must use it quickly, or it will break down into a mess.
If you happen to have an expensive, unlined copper bowl lying about, it is ideal for whipping egg whites. A happy reaction between the copper and whites generates a much more stable foam, with one-third more volume than you get in a standard bowl. Cookbook author Madeleine Kamman says you shouldn’t bother whipping egg whites by hand unless you have a copper bowl. (And if you do, scour it with a mixture of 1/4-cup vinegar and a tablespoon of salt, rinse it, and dry it thoroughly with paper towels before adding the eggs. Then omit adding any salt.)
Ms. Kamman says the best way to beat egg whites is with a serious stand mixer, such as a KitchenAid, Viking, or brand, is to add the salt and up to four whites to the bowl and beat for one minute at medium low speed. Add the acid, then beat for three minutes at high speed. If you need to add the sugar at the end, do so and beat for an additional 15 seconds at high speed. If you’re beating five eggs or more, the first stage should take two minutes, and the second should take three to four at a slower setting (medium/medium-high). If you’re using a hand mixer, beat the whites and salt for two minutes at medium speed, add the acid and beat for two minutes more at high speed. If you add sugar at the end, beat for 30 seconds.
How can you tell when the whites are done? Kamman places an uncooked egg (scrupulously cleaned) on top of the foam. If it doesn’t sink at all, you’ve gone too far. If it sinks 1/4-inch into the foam, your whites are perfect.