The Number One most important thing in homebrewing is sanitation. You can do almost everything else wrong and as long as your sanitation is good, you can still have a drinkable beer. You need to be religious about keeping everything clean. This point is reinforced in this article:

Both Tinsen and Lowry stress the most important aspect of homebrewing is sanitation. Everything that comes in contact with the beer needs to be sterilized. If it’s not, the equipment can become contaminated because of the yeast.

It’s a decent enough article, experts sharing tips with beginners, but no surprises if you’ve been homebrewing for awhile.

All my sanitation is done with bleach (unscented) and hot water. I always use a bit more than the guidelines on the bleach call for, and I’m paranoid about rinsing—I use the hottest water that will come out of the tap and often double-rinse. I haven’t had any problems with the last bunch of batches.

One time I did have a batch go horribly awry, it had to be a sanitation issue (everything else that could go wrong, did, as well): after a few weeks in the bottles, a thick, viscous something began growing in the bottom half of the bottle. Smelled horrible, tasted worse. I had someone swear it was botulism, but I don’t know about that. I ended up pouring it down the drain, the only batch I’ve ever had to dispose of.