The technique is pretty simple, but since it's a two-part pour a lot of people don't bother doing it. Pull the tap towards you until it is completely horizontal, and have the glass tilted at 45 degrees, until it is about three-quarters full. Like most brews, you'll want the liquid to hit the side of the glass nice and smoothly.
Now let it sit for a little less than 2 minutes, until the "surge" settles completely. Then, hold the glass directly centered under the faucet, and push the tap *forward* to complete the pour. That's it. A decent pint should have a head of about 1 cm and it should be creamy and consistent.
A good test is the "nipple" test. Jab your pinky slightly into the head and pull it out again. After having pleasured your Guinness like this, it will be quite excited and a little creamy nipple will remain on top. If it droops down again, your Guinness is potentially stomach-churning.
Don't be afraid to give your local barstaff a little lesson in this. You wouldn't accept an unmixed recording as your master tape, would you?