Growing up in central California, in a Mexican-Portuguese family, you would think that I would instinctively know how to make this. But, this was something we struggled with in my family. Our general recipe always called for lots of lemon and sour cream, and what resulted was a vaguely avocado-y dip of some sort. Not very memorable.
Years ago when we lived in San Diego I fell in love with the local version, which was just an explosion of real, creamy avocado flavor. I began watching local cooking shows, reading local recipes in the paper, and experimenting until I came up with my own version. The kicker? It's incredibly simple.
Basically, when you have good quality avocados, perfectly ripe, all that is needed is a small quantity of minced onion and salt. That's it.
It can also be enhanced with small quantities of minced tomato, onion, cilantro, and even jalapenos. But the quantity needs to be small - it's just to enhance, not overwhelm, the avocado. It has to be the star of the show.
Which is where most people go wrong - citrus. Citrus is a very strong flavor which just competes with the smooth avocado. Seriously, if you always use lemon or lime in your guacamole, try it without. You will be pleasantly surprised. The same principle applies to sour cream.
One of the biggest tricks for good guacamole is learning to recognize a ripe avocado. It should be thick skinned, preferably the Haas variety. The skin should still be mostly green - the blacker the skin, the more likely it will be overripe. It should give easily when you press your thumb into it, but not mushy.
I generally buy unripe avocados and let them sit out on the kitchen counter. Every day I check them, and when they are just beginning to ripen I put them in the fruit drawer in the fridge to slow the ripening process until I am ready to use them. You generally will have 3-4 days until they begin to go bad with this method.
I've always used the side of a spoon or a pastry cutter to mash my avocados. Most Mexican chefs will use a pestle, which is something I've always wanted. I finally splurged recently and bought my first one.