Students often ask me how they should learn new vocabulary. Many simply write down a list of words and their translation or spend hours upon hours on apps like duolingo, memrise, babbel or the like. The problem with both approaches is that, while they might increase their passive vocabulary, often for only limited period of time, the new words don't enter their active vocabulary. In other words, they can't use them when they need them.
In my experience, the best way to bridge passive and active vocabulary is the use of flash cards as shown below. Write the word you want to study- here "fahren"- in the middle of the card, and write anything that is interesting about the word grammatically at the top. Here, it is an irregular verb, so it is worth writing down its conjugation and past tense (Perfekt) form. This will help especially cognitive learners to remember the meaning of a word. Now, what is quite important when we try to learn a new word that we are keen to use in future is to write a sample sentence or two using the word in context. These sample sentences should be both self-explanatory and intuitive. If they are not, they are of little use. Finally, on the back of the card, you should write the translation of the German word into your mother-tongue. And last but by no means least flip back and forth to test yourself. Give it a try- you will learn many, many new words that you will be able to use and you are less likely to forget.