Show weakest words on login, and/or get a Reminder to practice when there are more than x weak words
I think one of the main problems is that sometimes as I advance I don't know which words I get wrong. I think duolingo could put the words separate from the big list of words in the vocabulary section, since it makes it is hard find. Also, I think everyday, as you log in or perhaps once in a while, it would be nice to see a popup screen or reminder that shows a list of words that are weak and also the option to practice them before going for the lessons. This could be added as a option, since it may annoy some people.
I know it exists, but lazy people like me never really go check the vocabulary. Besides, I've noticed there are many words that I forgot and duolingo still thinks they are strong. So in addition to weak words, maybe we can flag words we want to exercise and so it gives us the option to practise it immediately after logging in.