Spaced repetition (gespreide herhaling) is the most scientifically validated method for long-term vocabulary retention. The core idea: review a word just before you are about to forget it. Reviewed at exactly the right moment, the memory strengthens and the next review can be pushed further into the future. Apps like Anki (free, fully customisable) and Duolingo implement this algorithm — though Anki gives far more control.
Setting up Anki for Dutch: download the app, create a deck called Nederlands, and add cards. The front: the Dutch word with a sample sentence. The back: the English translation and pronunciation note. Add audio if possible — Forvo.com has native-speaker recordings of most Dutch words. Import pre-made decks from AnkiWeb (search Dutch frequency list) to start with the highest-frequency vocabulary rather than random words.
Best practices: do your reviews every day, even just five minutes. Never skip — the system works precisely because of consistent intervals. Add no more than 10-15 new words per day to avoid review avalanches. Add context sentences, not isolated words — Ik heb trek in iets zoets (I feel like something sweet) is far more memorable than just trek. For Dutch specifically, create separate cards for de/het nouns because gender is not predictable — force yourself to learn the article with every noun from the start.