To learn vocabulary, there are several systems, and 2 especially used in auto-learning :
- The lists (sorted or not by theme, by frequence). This is the vocabulary notebook our language teachers made us write in the secondary school, the notebook having for them the advantage that its form could be checked even though it was not learned… Because its use showed some obvious limits : The learned vocabulary and still to be learned staying at the same level, we cannot focus on the most difficult words.
- The flashcards, are these small cards with on one side the word in target language and on the other side the word in the origin language. The advantage is that once the word is known, you can remove its card to focus only on the others. Here is a more efficient method. But it is possible to do even better.
We saw that flashcards are a memorization mean through a repetition spaced in time. It happened that a German scientist, Sebastian Leitner, demonstrated in the 70′s that it was possible to maximize the system efficiency by sorting the cards in several groups corresponding to our memorization ability. This is the Leitner system and here is the functioning : We test our knowledge with the cards from one group. If we remember the meaning of the word, we put the card in another group and in the opposite case we put it in the first group. The time duration between each test increases with the groups.
For example, 
the proposed time durations being only proposals : We have 4 groups. The group 1 includes the words we hardly remember, the group 4 including the words we easily remember. We will check the words of the group 1 every day, the one of the group 2 every 3 days, the one of the group 3 every week and the one of the group 4 every month. If we success on the vocabulary of the group 1, the words we know are put into the group 2 and will be tested a few days later; the known words of group 2 will go to group 3, the ones of group 3 in the group 4 and the one of the group 4 will be considered as definitely known. On the opposite, the words of group 2, 3 and 4 we don’t remember would go directly in the group 1.
Thus you spend more time on the difficult words, you train your memory on the short term but also on the long term. The result is a more efficient memorization activity.
Original article : http://www.entre-france-et-coree.com/2008/05/12/du-bon-usage-des-flashcards-pour-le-vocabulaire/
More information on Leitner’s system : http://en.wikipedia.org/wiki/Leitner_system
