I've been growing basil for about 6 years now. Like many herbs, it benefits from frequent harvesting. I typically pinch the top growth off after it has at least 4-6 sets of true leaves. This encourages the plant to bush out. Since the first pinching doesn't result in enough leaves for pest, unless you are harvesting a significant number of plants, I chop these leaves up, mix them with olive oil and freeze them for adding to sauces later. Depending on the weather, in another 3-4 weeks, the plants are growing well and can be harvested as needed. Once the plant starts flowering, people often pinch off the flowers to encourage more leaf production. Once it begins to bloom, leaves will get smaller and the plant will get more spindly as its energy becomes focused on seed production. Pollinators love the flowers so I typically leave a few blooming stalks for the butterflies and bees. Also, this will allow your plant to set seed, which you can save for next year. This year, I have 6 basil plants and may allow one or two plants to set blooms, leaving the flowers completely alone and pinch the flowers back on my other 4 plants.