Mnemonic Key Word Method. Create an absurd image from the word you want to learn. You have to be somewhat creative but I find it is the best way to retain vocabulary.

There is a phone and computer app called "anki" it has a web page where you can download all sorts of flash cards. Or you can make your own. Every time you review a card it gives you an option on when you want to see it again. If the card was easy, you'll see it in seven days. If it was hard, you'd see it the next day.

I like using flash cards and reviewing them every night and morning a few times, it really gets stuck in your head after a while!

Make some flashcards using quizlet.com It will choose the flashcard you get wrong the most and ask you those more often. If you have a smartphone, they also have an app for phones. I like using it on my phone because I can study when I'm waiting in line or waiting for a bus.

listen to music. You can read the text of the songs and try to compare the words of the language you want to improve with the words of your language