I’ve had another wizard idea for learning grammar. You can find an online grammar lesson (on German separable verbs let’s say, like this one How to Use German Separable-Prefix Verbs), and import it as a lesson for your own use. You can then go through it, learning interesting grammar points, while you LingQ and tag all the new words, or just add new grammar tags to words you have already learned.
The advantage of this is that you can pick a lesson in your native language, whereas all the lessons in the LingQ libraries are in the target language only. Just remember not to click on Update Statistics or you will end up adding a lot of words in your own language to your target language scores!