BTW [member=19]bwarbiany[/member], my neighbors and I just bought a home brew setup and we're doing our first batch Saturday. We're going to get a couple extracts under our belt before diving into all grain.
Awesome, good for you!
Homebrewtalk.com is a great forum and resource.
My top three tips (outside of sanitation, because that should be #0!)
1: Yeast health. Make a starter with liquid, or use dry yeast. Most of what you do on "brew day" can be screwed up, but as long as you have healthy happy yeast, they'll do their job well. That means you need enough yeast to start out that they're not stressed during fermentation, because that will lead to off flavors. So make sure you have enough yeast!
2: Fermentation temperature. Again, this is about keeping your yeast happy. However you have to do it, try to maintain fermentation temperatures in the 60-70 degree range for most ales. Note: that's *beer* temp, not ambient. Fermentation generates heat, so having one of those stick-on thermometers on your fermenter will tell you what the actual temp is. There are tons of ways to control temp (some are very cheap, i.e. putting the fermenter in a tub with water and rotate frozen water bottles to keep the temp in range), but this is one of the most important things I can stress about brewing delicious beer.
3: Water. This is less important since you're starting with extract, but the ENEMY in either extract or all-grain is chlorine/chloramine. If you don't know anything about your water, go buy distilled or spring water. If that's not an option, buy campden tablets, which will neutralize chlorine/chloramine in the water immediately. Frankly if your tap water tastes good, it's ok to brew with, but only after handling chlorine/chloramine. That will ruin your beer.
BTW if your beer kit instructions say to do a 1-week primary, 2-week secondary, etc. you can ignore that. No reason to use a secondary for most beers. Just keep it in primary 2-3 weeks, then bottle.