Frighteningly detailed guide to frothing milk over at coffee geek. For beginners, though, perhaps it’s better to think about it more simply.
Start with cold milk, in a metal jug with a pouring spout. No more than half-full.
Remove any “froth enhancing” elements on your steam wand – they’ll over-lift the milk, and it won’t have a chance to heat up properly.
Two phases to frothing the milk: making the texture, then heating the milk (if it still needs it).
To make the texture, aim the steam just at the surface of the milk; it should move around like a whirlpool if you’re holding the jug at the right angle: you may need to tilt the jug a little.
Once the milk has the right texture (you’ll need to experiment to work this out: if it looks like dishwashing foam, you’ve put in too much air), move on to heating the milk: put the steam wand below the surface of the milk. Either use a thermometer, or keep your hand at the base of the milk jug: when it’s too hot to hold comfortably, it’s about ready.
Pour carefully: not too much distance between the jug and the cup, and don’t pour too quickly. Experiment with moving the jug to create latte art (a skill in itself).