Best Fixes
Fetch the remote changes, then merge or rebase your local work on top of them.
Push again only after your branch includes both the remote work and your local commits.
Error Fix
How to Fix a Non-Fast-Forward Git Push
Why Git rejects the push and the safest way to catch your branch up.
A non-fast-forward push means the remote branch has commits your local branch does not have. Git blocks the push so you do not overwrite remote history by accident.
Avoid This
Do not default to force-push unless you are intentionally rewriting history and understand the branch ownership.
Do not assume the remote change is irrelevant without checking who pushed it and why.
Save commands, add notes, and build a Cheatbook with the fixes you want to keep handy.