I keep meaning to post in this thread since outside of music brewing is just about the only other thing I pour as much time/money into. I've lost count at the number of batches we've done over the past couple years but it's safe to say that there's always at least 10 gal. fermenting and then another 5 gal. bottle conditioning. If you're just starting out with pre-hopped kits a few really easy things you can do that will help the taste of your beers are
- making sure the temperatures are as stable as possible when you're fermenting. Yeast doesn't like large temp. swings. A couple degrees is fine, but if it's more than 4 degrees Celsius you may want to consider moving it.
- make sure the wort is either in a very dark place, or covered with a blanked while it's fermenting. Sunlight can introduce some off flavors.
As far as home brew beer, definitely only use distilled water.
- don't listen to this. One of the most important ingredients in your beer is the water. If your area has decent drinking water then the mineral count in the water can bring some really nice flavors to your beer. If you're really serious you can get a water report from your city which will tell you whats in it, and most homebrew books have a good rundown of what different minerals will bring to a beer. Distilled water is fine, but you could be really be missing out by using it.
If I can find some, I'll post some pictures of the setup we use at home. It's not super fancy but it works.
Also one of my favorite brewing sayings:
Give a man a beer, and he wastes an hour, but teach a man how to brew, and he wastes a lifetime.