A beer "head" of foam is, like most things in life, an example of perfect balance; too much and its undrinkable, and if not enough, you can't full experience the unique compounds of a given brew.
I learned this technique through working my way through college as a server, but I've seen it go awry enough (especially after a glass or two already) that I'm happy to share this helpful how-to from The Art of Manliness.
Jeremy Anderberg says, " When properly poured, the beer produces aromas and flavors that can only be present at the right conditions, and with the agitation of a proper pour...The process for pouring beer into a pint glass is the same whether you’re doing it from a bottle, a can, or a tap. It’s also the same no matter the style of glass."
Check out the photo tutorial in full at The Art of Manliness: How to Properly Pour Beer