How I do itWhen starting out there's some tips that will make you better beer using extract:
1) ferment in glass carboys, glass is easier to clean, doesnt scratch as easily as plastic, thus reduced chance of infection, plus fun to watch!
2) after fermenting, rack to a second carboy for beer to clear
3) use liquid yeast like Wyeast
4) make a starter
5) control your fermentation temps: 65-72F for ales, 54F or so for lagers, I use temp control on a merchandisser fridge to ferment. Got 5 gallons of ale fermenting at 68F now
6) use some type of grain even with extracts: step a 1 lb or two of crystal malt
7) do full wort boils if possible, this means a 6 gallon pot at minimum for a 5 gallon batch, 12 gallon vessel for 10 gallon batches, 7 and 15 are better however. This also means you'll probably have to brew outside, which is a plus
Eventually you'll want to move up to all gain brewing, kegging to eliminate bottling, temp controlled fermentations. It's sort of like reloading: you'll have more $ invested in equipment but the cost of each batch of beer comes down. Grain can be bought for 75 cents a lb, a 10 gallon batch uses 20-22 lbs of grain, or about $15 of grain, that's about 3 lb of liquid extract nowadays and for a 5 gallon batch you'll need 2 cans of liquid extract.