What can you expect content-wise on those other platforms?
Both of them show links for new blog posts when I publish them on here, for starters.
My Tumblr tends to have a lot of reblogs of things I like, so mainly pretty pictures, funny things, cats, motivational posters/images.
My Twitter shows my GoodReads updates, as well as probably a bit of “photo journalling” of my everyday life (this is something new that I’m going to start trying to do regularly). I’ll also occasionally retweet things, but not hugely often there.