1) I don't believe you. You're a fine writer.

2) Writers write. So write more. The only actionable advice I ever got.

I used to devour howtos like Bugs In Writing. https://www.goodreads.com/book/show/601222.Bugs_in_Writing

Once I felt confident that I'm saying what I meant to say, I think I stopped. I should probably revisit the classics for a refresher.

3) Simple is harder. Explaining complex stuff is a ninja power. Just keep at it.

4 bonus tip) Proofread, edit stuff you wrote 3, 6, 9 months ago. Consciously note how your writing skill and voice have changed.