Spaced Repetition
Reviewing at growing intervals — a day, a week, a month — timed to catch memories as they fade.
Spaced repetition schedules reviews at increasing intervals, catching each memory just as it starts to fade. Reviewing a word tomorrow, then in three days, then in a week beats reviewing it three times today, because each spaced retrieval happens after some forgetting and therefore strengthens the memory more.
Dedicated apps automate the scheduling per card. A simple version, review new words daily, older bands weekly, works nearly as well at the 1000-word scale and is much easier to stick with.