I use Anki for learning/improving Japanese.

I have installed a community "deck" that has thousands of Japanese words written in kanji. You see a sentence were the word is used and then you click to see the meaning, then you are displayed an image illustrating that word and you can hear the audio recording of the sentence. Below there are other example sentences where the word is used. When you are finished with the word you self-evaluate how difficult it was, and move to the next word which is either a new word or a word you already saw before (displayed based on your self-evaluation)

I used Anki successfully for a while, but after the novelty wore off I went back to using paper index cards. I was already doing spaced repetition with the flash cards anyway, and I can work much faster with a deck in my hand. I can also pull them out and study them on the bus or in front of the TV without having to fire up my laptop or phone.

I also use a quiz program which requires me to type in the answer and spell it correctly. This forces me to focus, while with Anki my attention would begin to wander after a while.

One advantage to Anki is that the newest textbooks often have pre-made Anki (or Quizlet) decks for each chapter that you can download from the book website.

I have used Anki for more than a year.  It is very good.  It is an efficient way to memorize vocabulary.  I used it in a very similar way as shown in this video https://www.youtube.com/watch?v=o5ccduvnGZ0&t=1s  Anki: What it is, how to use it (to learn a language)  I think recording words you want to make sure to remember at the time your first hear them is better than using a shared deck.  

One thing I have started doing is putting more emphasis on learning words in context.  Instead of simply putting the word on one side and the definition on the other, I include a sentence or at least a phrase that uses the word in it.

I also learned the hard way that it is better to make the front side of the card in your native language, so you have to actually remember the word in the target language, .   I started out putting the Spanish word (target language) on the front.  I found there were lots of words that I knew the meaning of when I heard them or saw them, but I couldn´t remember it quite well enough to say it properly in speaking  (¨let me see, was that vientre or viento¨?).  It is more challenging to put the word on the front of the card in your native language and have to actually remember every syllable of the word instead of just recognize it when you see it.  

I like Anki because of the ability to syncronize your set of cards across several devices: I have a desktop computer, a laptop, a tablet and a smartphone and installed Anki on all of them; by synchronizing (which requires you to register, but it's free and you're still the only one using your deck) I can pick up studying wherever I stopped no matter what device I'm using.

What I found difficult (and still do at times) was getting used to the words for the functions in Anki (cards, decks, notes...) and making my own decks with additional fields for pictures, examples, etc. But once you know how it works and have everything set up the way you need it, it's worth it because Anki can be quite powerful.

I agree very much with Susan that learning vocabulary without context isn't always useful. It's extra work to always include an sentence as an example, or maybe a definition, for every word but it's worth it. I learn vocabulary in both directions, that is, language A -> language B and language B -> language A. Anki makes that easy. It's one thing to understand the meaning of a foreign word, the other side of the coin is using the word.

Like Evil Eye, I also use another program which requires me to type the words correctly. I've found that I learn words which I don't remember easily in Anki better if I have to type it; and, after all, if you want to write something, you'll need to know how to spell the word, too.