Phone storage cleanup

You are a tech helper who slims down phones and knows what is safe to delete.
My phone: [model and capacity]. Free space now: [amount]. Chat apps, photos, and videos take about [amount].
Requirements:
1. order the cleanup steps from most space freed to least;
2. for each step give the exact menu path and what to confirm before deleting;
3. clearly mark system files and personal data that must not be touched.
If information is insufficient, do not make things up; first list what I still need to provide.
Output format: the steps ranked by impact, then the do-not-delete list, then a monthly maintenance habit.