1. Ingredients: The first extract tip is one of the most important. Always try to use the freshest ingredients you can get when extract brewing. If your local homebrew shop can't supply them, then get them online. Their turnover is so high that you are virtually assured that their products are fresh. Use DME instead of sugar in your extract brewing recipes, you'll get a fuller richer flavor with just as much attenuation. Try substituting liquid or dried malt extract in place of sugar for priming for a thicker head. Always use the ingredients from the beer's country of origin. If you are making an English Bitter, use an English Pale Ale Malt as your base malt. For that authentic American Microbrew taste, use American Malt Extract and American hops and yeast. When making Belgian beers that call for Candi Sugar, don't use the crystallized rock candy sold as Belgian Candi Sugar. They now have authentic Candi Syrup from Dark Candi Inc., at many homebrew outlets. This is the same sugar used by Belgian breweries. It comes in at least two grades, dark (D) and darker (D2). It will give your beer that distinctive Belgian flavor. A couple of tricks to lighten your extract beers are: adding the majority of your extract the last 15 minutes of the boil, or boiling for 45 minutes instead of an hour to reduce the Maillard reactions in the wort. For an extract beer with more body, try adding 4-8 ounces of malto-dextrin powder during the last 15 minutes of the boil. Choose your recipes carefully. Just because it's on the internet doesn't make it a good recipe. Quite a lot of them have never been brewed before. Check out some of the brewing books, especially Brewing Classic Styles by Jamil Zainasheff and John Palmer, soon to be a classic and How To Brew by John Palmer, already a classic, both are "must haves".
2. Water: Try to carbon filter your brewing water. It's easier than using a RO unit and adding back all the minerals. You can use bottled spring water but in the long run, the carbon filter will pay for itself in savings. Don't use distilled water unless you need to dilute your hard tap water. Get a water test done at Ward Laboratories, Inc. It's cheap and you can make adjustments to your tap water if it's too hard or you want to brew with the beer's water of origin. Order the W-6 test, currently at $16.50, very reasonable. Find out if your tap water is treated with chlorine or chloramines. It makes a difference. You can boil off chlorine, you can't boil off chloramines. According to John Palmer in How To Brew you can add one campden tablet (found at all winemaking supply stores and online) to remove the chlorine and chloramines from up to 20 gallons of tap water. You can also use bottled water. Even the best carbon filters won't filter out chloramine due the chlorine-ammonia bond. If you are having problems with mash pH, try Five Star's 5.2 pH stabilizer. It buffers the pH at 5.2, ideal for brewing water.
3. Yeast: Use liquid yeast if you can. You get more choices and you'll make better beer. Always make a starter for beers with OG above 1.050 and try to pitch while the yeast is most active. Plan your brews so you can reuse the same yeast a few times. As soon as you rack one beer to the keg or bottles, the cell count of the yeast in the bottom of the fermenter will be close to what the commercial breweries use. I wouldn't go more than 4 or 5 times though. And try to start with the lighter gravity beers and work up to the darker higher gravity beers. If your local homebrew shop can't get fresh viable liquid yeast, and you are forced to purchase it online, order it from the store that is closest to your home. This is especially important in the summer months when the yeast have to travel long distances in super heated trucks. Purchase as many different strains as you can afford to reduce per item shipping cost and have them shipped at least 2-day shipping with an ice pack. Don't order three or four ice packs because you take a chance of freezing some of the yeast next to the ice. Add a good yeast nutrient such as Servomyces by White Labs to your extract beers. The little bit of extra money is nothing compared to the overall cost of the other ingredients. It makes a difference.
4. Buy a good brewing software. Use it to change or adjust your hop additions based on the variety's alpha acid content. You can adjust hop additions based on full wort boils and the increased utilization they offer. Use the full wort boils when you want to lighten your extract beer but remember that you'll have to use a chiller to get the temperature down in that much wort. Use the software to build your own recipes and stay within the BJCP guidelines. Brewing software can convert all grain recipes to extract, scale up or down a recipe based on your efficiency, and do all the math for decoction mashes, batch sparges, and multiple infusion mashes.
5. Hops: Don't be afraid to switch the hops from the recipe. Experiment, there are a lot of really great hops out there. Some of the higher alpha acid hops also have great flavor characteristics. I used Simcoe hops in my American Barleywine as a dry hop. Simcoe was bred to have high alpha acids for bittering, but it's low cohumulone levels make it a good hop for aroma and flavor. Extract kits are hopped on the conservative side and hopped extracts lose some of the flavor when the malts are produced. If you want more bittering hop flavors, you can boil the hops in water for about 30 minutes and add this to the extract boil. Adding hops at flame out adds some flavor but mostly aroma. For a more robust hop aroma, add hops to the secondary and dry hop until the beer is kegged or bottled. Make sure you use the appropriate hop for the beer style you are brewing.
6. Chilling: If you can afford it, get a pre-chiller to pre-chill the water going into your immersion chiller. The faster you can get the temperature down below 80 degrees, the more cold break proteins are produced and the better your beer will be. Try not to agitate your beer too much when you begin using an immersion chiller. It's tempting to stir the heck out if it to get more beer over the coils to get the temperature down quicker. But, you run the risk of hot side aeration which shortens the shelf life of your beer. Once the beer gets below about 90 degrees it's alright to start stirring more vigorously to chill faster.
7. Sanitization: Don't use bleach to sanitize, ever. Use StarSan or one of the other no rinse sanitizers. Make sure everything is thoroughly cleaned before you sanitize. Sanitize before you use your equipment, then clean and sanitize it again after you use it. Get in this habit and you will make better beer. Any plastic buckets you use post boil need to be replaced every 4-5 brews. I know, that sounds crazy but that's just the way it is. Unless you use sponges to clean and never touch the sides while stirring, it's too easy to scratch the inside of these plastic fermenters. Once they are scratched, it's very hard for the sanitizer to get into the bottom of the scratches due to the surface tension effect of the water phase. Use your carboy to ferment in instead, and use a blow off hose just in case. You can watch what's going on better through the glass. The only problem with glass carboys occurs when you want to top crop your yeast for use on another batch. You just have to reuse the yeast from the bottom of the fermenter after fermentation has ended. If you are worried about the trub and hops residue, wash your yeast.
8. Fermentation: Pay close attention to your fermentation temperatures. Place the temperature controller's probe on the side of the fermenter, tape it on, then insulate it with some bubble wrap. You want to measure the temperature of your beer, not the ambient temperature inside your fridge. I know some Trappist breweries ferment at 80+ degrees, but they have a whole different set of conditions which allow them to do so. I don't think you can duplicate these conditions at home. It's better to ferment at a reasonable temperature and let the yeast stay clean and happy.
The format and some information for these extract tips was adapted from an article by Drew Beechum of the Maltose Falcons. Other information and extract tips were gleaned from reading just about every brewing book available and listening to all the podcasts on The Brewing Network.