I recommend a vocabulary learning website such as this one:
This website uses spaced repetition software, this means that the words will appear more frequently depending on how often you get them wrong.
I found this website to very useful for me while studying Korean. Thanks to it I have also learned how to type in Korean. You can find liits of vocabulary or even make your own
There is also Anki. With Anki you may design the way you want to learn new words. That is, you make your own list of words and meanings. You could choose to have a word presented and then you have to remember its meanings. Or, you could create some sentences with a blank that must be filled with the word you are learning or a synonym. I recommend giving as much context as possible, by providing long sentences, instead of learning isolated words and meanings.
I took a quick look at LingQ as @John suggested. It could be a good option, but I don't like the fact that you work with translations instead of using the target language.