There are two approaches to growing sweet basil: as a culinary herb or an ornamental plant. Basil is very attractive as it develops large, puffy leaves and tiny white flowers. But if you are cultivating basil for cooking, it's best to fool Mother Nature a bit. The best-tasting leaves are fairly small, and picked before the plant flowers. I think it's best to grow basil in containers because you can bring in the plants if the temperature drops below 50°F.
Basil seedlings just need water and full sun until they reach a height of about seven inches. If the plant is healthy — and not newly transplanted — grab your clippers and cut back the main stem about an inch. Pinch off the largest few leaves, then let the plant recover for a couple of days. Then start pinching off new growth tips forming in any clusters with six or more leaves. This will encourage growth of new side shoots for a nice, full plant. As the summer progresses, watch for flower buds - you'll want to pinch them off immediately. If you allow the plant to flower, the leaves will become bitter and the stems turn woody. At some point it will be difficult to keep up with the flower buds; if you have a long growing season, consider a drastic pruning of all stems down to about three inches. You'll be rewarded with a new crop of leaves in a two to three weeks.
If all this seems like too much trouble, basil plants do just fine without much manipulation. You can do staggered plantings to ensure a good supply of tender leaves. Just keep an eye out for the first frost, as that event will kill your basil overnight.