Going back to flashcards
At the beginning of your language learning, trying to learn a lot of vocabulary might not be that helpful or easy. If you can’t actually use this language in real sentences and constructions, it will be even more difficult to remember. But at some point in your language learning career, you are likely to feel that you don’t have enough vocabulary. You will have enough sentence structures to want to fill them in with useful (and/or random) words. This is when the word lists and the flashcards will come in handy.
It may feel like you’re back in primary school, but reviewing flashcards is a good way to get more exposure to your words and help you remember them. If you go the old fashioned route and make them yourself, the actual process of making them will help reinforce the knowledge. Try to keep a pile of flashcards with you at all times, so if you have a few minutes to spare, you can go over them.
If you are doing electronic flashcards, again try to keep them mobile. If you can put them on your mobile or other portable device, all the better. Just remember to keep looking at them!
Supposedly if you see and use a word 9 separate times, you will have no problem remembering it forever. See how much of your spare time you can use adding extra views to your vocabulary lists!