Interesting! Writing is not something i would have thought to do. Any tips on vocabulary? I assume reading, and i suspect my normal technical reading (programming related books) is less helpful than reading for leisure.

Anecdotally, I think a lot of my vocabulary came from reading older novels. J.R.R. Tolkien, C.S. Lewis, Issac Asimov, Arthur C. Clarke, Agatha Christie, Sir Arthur Conan Doyle, etc.

Recently I've started reading modern scifi/mystery novels and found the vocabulary to be very simple (smooth? Like the text is lacking texture) by comparison.

If you can't get through novels without falling asleep, try audio books (preferably unabridged). Lots of classics on https://librivox.org

I'd say an even balance of writing and reading. For reading content I think anything that's interesting to you and published would be helpful. Technical reading is better than nothing, but not very fun to read generally.