With regards to the beer, 4 things primarily determine the amount and consistency of head:
- Types of malt used: light malt typically produces larger, more dish-soapy bubbles. Roasted or dark malts will typically produce smaller bubbles. The proteins in the malt are what determine the consistency of the bubbles. There are additives that can alter and enhance the head forming capabilities of the beer. These are usually forms of protein. One of the best silky mouth feel beers I've ever had is Flying Dog Pearl Necklace Oyster Stout. Yes - they actually add oysters to the brew. The protein makes for an amazing feel.
- Amount of carbonation: pretty self explanatory. Mo' gas, mo' bubbles. Higher ABV beers and very malty beers can sometimes hold almost no CO2. Give these a rough pour to produce a decent head.
- Type of carbonation: CO2 produces larger bubbles while nitrogen produces very fine small bubbles which gives Guinness its famous silky creamy head.
- Conditioning & storage: bottle conditioned beer will hold more CO2 and have a different head and mouth feel and coarser bubbles. kegs carbonated by pressurizing with CO2 will hold less and be a bit foamier.
With regards to the pour, if less head is desired, tilt the glass at least 45 degrees and pour slowly, on the glass, rising as you pour to always be pouring just above the level of the beer. For more head, well... dump 'er in.
The glass will make a difference too. For some high-browed beer-snobbery about cleaning your beer glasses: http://byo.com/porter/item/425-can-you-explain-the-dos-and-donts-of-cleaning-beer-glasses