1. Don't try to memorise word lists, but learn the words in context. You can read several texts about the same or similar topics and important key words will show up several times. This way you will remember them automatically. For instance, if you want to learn sport related vocabulary you could read articles about the Olympic Games and the names for the different kinds of sports as well as general words like athlete, stadium, record, medal, team and so on will show up.
2. Use the new words by talking and writing.
Let's stay with the example of sports related vocabulary. You could talk with a friend about sports you do yourself or like to watch. And you could write a notebook entry about your opinion about the Olympic Games in Rio.
3. If the words are hard to remember, try to create mnemonics.
Some ideas how you can use mnemonics for learning English can be found here: https://www.oxford-royale.co.uk/articles/mnemonics-memory-aids-english-language-rules.html.
4. If you want to use flash cards, you can use a program like Anki with spaced repetition and this way you can also review the vocabulary comfortably on your smartphone.
Do not learn words in isolation, but as phrases, and make sure you practise pronouncing them. For example, if you hear a good expression in a film, pause it, listen again, and then repeat many times, trying to sound exactly like the actor who said it.
And of course, I agree with Francisco: repetition is the key!