Repetition is essential to remember words over the long run.
See the term “spaced repetition” in a Wikipedia article:
This technique is not easy to implement, but with a little discipline and organization you can make it work. If you are using flash cards for example, you can make it a rule to review the flash cards you mastered after a week, or a couple of months. It is not a big deal to repeat those cards you are supposed to know, and check to see if you still remember most of the words as you test your confidence in your real knowledge of the language.
The thing you will achieve is reinforcement of your vocabulary skills. You certainly have experienced perfectly mastering perfectly a set of questions for a school exam and then forgetting most of them after a few weeks. The issue with language need not be passing another school exam on a specific day, but being ready to engage in an impromptu conversation.
What you really want to do when learning a foreign language is more than being ready for the next school test. If you learn new vocabulary with a newspaper and dictionary, it is a good idea to go back to last month's articles with no dictionary and see how much you understand. If you are learning with another method like Pimsleur, the tape will take care of the repetition since it is a basic principle of their system which is called “timed interval repetition”. Words learned with spaced repetition usually stick to your memory, provided you do your homework on a regular basis, with discipline.
This is why we are using a variant of this method as a key part of the learning sequence in our Language Tutor as opposed to most flashcards programs, which we believe provide a rather superficial learning.
How to learn vocabulary and why?
Mastering vocabulary is a difficult and time-consuming task but necessary and probably the most important part of the language learning process for many reasons. Just listen to the radio or watch a movie in a foreign language or try to follow a conversation and you quickly realize how much you do not catch or understand because of all the words you miss. You need to practice and acquire more vocabulary, because knowing the basic of the grammar and the words you learned at school or through any language learning method is simply not enough.
Words have many false friends in any new language and they also have confusing spellings. The rules of pronunciation are full of exceptions and all of that add up to the difficulty of the process.
People rely on memory and realize that a known word cannot be retrieve when needed, unless it has been well "imprinted' through a long, sometimes mysterious and often erratic series of steps.
This is why, decades of learning experience and long hours spent in practicing vocabulary, led us to refine our methodology for learning vocabulary, and there it is coming soon in a dramatically efficient package with many features you will most likely appreciate.