Drink, drink, drink,
Besides the other great advice, find a store that allows for doing mixed sixers of micro brew, it's a good way to try different styles and it's often a couple bucks or more cheaper than buying an entire sixer of one micro...for example I can get a six pack of bell's two hearted for about 12 bucks...but at the same beer store they have a cooler for 9.99 mix and match....and you never know what they will stick in there...so if I'm not in the mood for something in particular or feel like expanding my horizons and not risking an entire six of something I might not like.
So far I've only had a couple bottles of something that I could say I wouldn't have again.
But I've also discovered a bunch of new breweries that I might not have if their beer was in the 12-15 dollar a six.
And I've also gotten turned on by a few beers in styles I never thought I'd try...Like Vienna Lagers....I've never been a fan of the fizzy yellow type of lagers, but damn those brown, malty Vienna ones are fantastic.
If you have a Trader Joe's in your town they usually allow for mixed sixer filling as well. And those are 5.99, and the majority of the "TJ's" labeled beers are brewed by Gordon Biersch.
Usually if it is a beer I have never tried or even a new style then i will sit down with the beer and google and do some reading on the beer or the style.
Usually beer advocate will have the beer reviewed, and also a lot of the micro breweries have info on their website, sometimes the actual recipe or at least ingredient info.
Another good resource is the BJCP style guide, it gives a lot of info on the beer, the history of it, the numbers range for OG, FG, IBU's, etc. As well as a list of commercial representations of the beers.
BJCP 2008 Style Guidelines - Index
Then if I am planning to brew something, I usually google to see if there are any clone recipes for the beer online.
Sometimes I will do a themed sixer, like all IPAs or Ambers or stouts, and get six different beers of the same style. It is a good way to see how different breweries tackle the same style...then if I mamnage to find info on the online, or even clone recipes I can see what ingredients are similar between recipes, and what is it that gives a certain version something special...i did that with vienna lagers, and learned a lot about the style,
Hope this helps.