It has already been noted that a learner needs to re-encounter a new item

It has already been noted that a learner needs to re-encounter a new item several times in order to remember it permanently. Very common items like go, put, person, day are likely to be met again in the course of texts or interpersonal communication anyway. But as soon as you start expanding taught vocabulary to include even slightly less common items like business or cook, this becomes less and less likely, and we need to create opportunities for review. This means using effective learning tasks whose focus is multiple, meaningful encounters with the target items. Probably every lesson should include some vocabulary review work.
        A useful principle here is that of "expanding rehearsal". The most effective review takes place when students still remember the item but need a slight effort to recall it. So do the first review very soon after students have learnt the item—in the next lesson, for example. The next review can be after a longer gap— perhaps a week. Then two weeks, then a month and so on. As students learn the item better and better, the length of time they can remember it without a reminder grows, as does the speed at which they can retrieve it when needed, until they get to the point at which the item is part of their permanent vocabulary.