1 Go for plain, dark or milk. Chocolates with flavourings or fillings or decorations taste mainly like whatever flavouring or filling or decoration has been used and will teach you nothing.
2 Be ready to spend a little more than on your usual bar. As with wine, cheese or olive oil, fine products are more expensive. Expensive doesn't mean good, but good is seldom inexpensive.
Enough said - you get what you pay for, for beer as much as for chocolate. If you can't get over paying more than $10 for a six-pack, you'll be doomed to drink MGD forever.
3 A tasting will enlighten you only if you compare similar products. So, for instance, taste 2-4 bars of plain dark chocolate from Venezuela or, even more acutely, from one region of Venezuela, such as Sur del Lago. Compare dark and milk chocolate only if they're made by the same brand with the same beans (Mangaro milk and dark from Michel Cluizel, for instance). Or bars made through similar processes - those begun from the bean, from cocoa liquor, from melting bulk chocolate; http://www.seventypercent.com/ is a good place to go for more advice.
You will learn more about the nuance of beer comparing different American IPAs against one another, for example, than you will comparing an American IPA against a Belgian Dubbel.
4 Ethical values. You are exploring the world of chocolate (taste, texture, style), not trying to save the world. Organic/fair trade chocolate is only a very small part of chocolates you can explore.
Organic and "green" beer are over-rated, drink what tastes good!
5 Healthy chocolate. All chocolate made from the basic ingredients - cocoa beans, sugar, cocoa butter, lecithin, and natural vanilla - is healthy if eaten in moderation.
Increasingly the evidence shows that moderate drinking is healthy. Doutre-Roussel maintains a shockingly petite figure despite eating a ridiculous amount of chocolate on a daily basis. The key? Exercise and awareness - key if you want to avoid your passion for craft beer leading you to a beer belly.
6 Check sell-by dates and the temperature of the store. You can never be entirely sure, but you can reduce the risk of buying stale chocolate, or chocolate that has suffered from variations in temperature, by not buying in a shop kept at more than 23C.
Like good chocolate, beer should be kept fresh and stored properly: cool, out of bright light, and (depending on the style) not for too long.
The comments on tasting are useful as well, though I will let you read and draw parallels yourself.