While some linguists will say that drilling down on and understanding grammar has more effect on language learning than others, there is no doubting that it is important on some level. The folks at All Set Learning have already done a great job compiling an outstanding grammar resource for Mandarin learners with the Chinese Grammar Wiki. The Wiki has compiled grammar patterns and vocabulary from multiple learner textbooks as well as other sources and distinguished them by level. Though I haven’t used this extensively, I do feel that incorporating review of these grammar points could be a very good writing activity.
Another resource that may be of interest is a character frequency list such as this 3000 character list I used quite a bit in my early studies. There is also this list of 1000 characters with links to each character’s dictionary entry and collocations. I’d be interested to learn more about how others use this type of list in their studies.