You might want to wait until they are about 6 inches high, then remove the top few leaves until there are just one set (2 leaves) on that stem (prune back to a set of leaves just above where a stem forks). Note that this does not apply to bush basil (such as ‘Spicy Globe’), which have much tinier leaves and many more along the same length of stem. Prune these back to keep their shape, leaving at least 3 or so sets of leaves. For both types of basil, always prune out any developing flower buds.
You might want to wait until they are about 6 inches high, then remove the top few leaves until there are just one set (2 leaves) on that stem (prune back to a set of leaves just above where a stem forks). Note that this does not apply to bush basil (such as ‘Spicy Globe’), which have much tinier leaves and many more along the same length of stem. Prune these back to keep their shape, leaving at least 3 or so sets of leaves. For both types of basil, always prune out any developing flower buds.