The nice thing is that you can apply this technique to all forms of carbonated liquid which gives you lots of opportunity for practice. Of course, sodas and other carbonated drinks wont get a head on them like a beer.
To really enjoy a beer, it must be the right temperature, have a good head (foam at the top of the glass) if appropriate, and still have proper carbonation as you begin to drink. It cannot be watered down from ice, or flavor tainted from a glass that smells of dish soap. Also, a clean glass is really the only way to fully enjoy a beer as it was intended, no plastic party cups!
Step 1: From Wikapedia About Serving Temperature
The temperature of a beer has an influence on a drinker's experience. Colder temperatures allow fully attenuated beers such as pale lagers to be enjoyed for their crispness; while warmer temperatures allow the more rounded flavours of an ale or a stout to be perceived. Beer writer Michael Jackson proposes a five-level scale for serving temperatures: well chilled (7C/45F) for "light" beers (pale lagers), chilled (8C/47F) for Berliner Weisse and other wheat beers, lightly chilled (9C/48F) for all dark lagers, altbier and German wheat beers, cellar temperature (13C/55F) for regular British ale, stout and most Belgian specialities and room temperature (15.5C/60F) for strong dark ales (especially trappist beer) and barley wine.
There is no way I could have said it better! : )
PS - the thermometer is just to emphasize this step is about temperature, dont use one like the one in the photo.
Step 2: Prepare the Glass!
Im told this applies more to cheaper beers that may be bitter if allowed to warm up to a cool temp vs downright cold. This makes sense, your taste buds actually numb from cold.
If you want less head and more carbonation, you can give the glass a quick rinse with water and do not dry the inside, just a quick shake out of the excess water. The moisture will fill many of the microscopic pores of the glass buffering the carbonated liquid so that the carbon dioxide is not as easily released. Basically a damp glass keeps more carbonation.
Never use a warm glass, room temp can be ok, but never warm like out of the dishwasher. If you want a quick chill and lots of carbonation, toss a few ice cubes in the glass and swirl until it feels chilled. Quick shake the excess water out when you dump the ice.
An alternative if you have just removed a warm glass from the dishwasher would be to rub an ice cube on the outside of the glass only to bring the temperature down to a reasonable level. This preserves the dry surface inside and will give the beer a better head.
Note that some beer "experts" will insist that the thin layer of moisture in the glass will dilute the flavor of the beer and should never be allowed. I personally feel that the few drops of water will not make a significant difference, after all, we are shaking out as much as we can first.
Step 3: The Big Moment
Take aim at the halfway point as you pour along the side of the glass. This is a gentle process, dont rush. Dont let the can or bottle do the "blub blub blub" thing, the stream of liquid should be smooth as it hits the glass and not jumpy. Take your time with this part of the process.
As you cross the halfway point, you no longer need to run the liquid down the edge of the glass. You can start tipping the glass to a more upright position.
If you want less head on the beer, try to maintain the flow down the edge of the glass longer as it fills. This is something that will require lots of practice and is best practiced on a day off. ; )
If you want a big head of foam, simply make sure the glass is dry inside, room temp, and then pour quickly right to the bottom of an upright glass. This is actually recommended for some Pilsners to give them a characteristic head that flows over the top of the glass.
Step 4: Experience the Beer!
No photo here, as it is best to imagine yourself enjoying your favorite brew.
Step 5: Cheat Sheet
Ale -------------------- 1 finger thick -------------------- room temp or cool, pour along the side for whole process, glass can be moistened inside to minimize head
Stout ----------------- 2 finger or more ------------- room temp or cool dry glass, pour along side to half full then let it rest for a moment before finishing with the glass straight up
Pilsner -------------- over 2 fingers ----------------- room temp or cool dry glass, pour into straight up glass
Can Beers ------- less than a finger ----------- cold glass, rinse, pour along side for whole process