If you haven't read "The Mom Test," stop building and read it this weekend.
It's about how to talk to users without them lying to you to be nice. Single biggest fix to how I do customer interviews.
Found a goldmine: Refactoring UI is still the best resource for devs who design.
Read it 3 years ago, re-read last week, learned new things both times. If your project looks "developer-made," start here. Not affiliated, just useful.
The biggest lever for my retention wasn't a feature. It was the empty state.
New users opened to a blank screen and 70% never came back. I added one pre-filled example and a single line of copy explaining what to do next. Retention doubled. No new code, just less confusion.
Look at your empty states. First thing every user sees, usually the last thing we design.