Find them all first
Scan twelve months of transactions rather than one, because annual renewals are the ones that hide. Check every card and every account, including the one you keep for a single direct debit.
Write down the amount and the cadence for each. The monthly total is usually the moment the exercise becomes motivating.
Sort into three piles
Used and worth it: leave alone. Not used: cancel now, today, while you are looking at it. Used but duplicated: three streaming services watched one evening a week between them, two cloud storage plans, overlapping software. That middle pile is where the money is.
Make the next one easier
Set a reminder a week before any annual renewal above a threshold you care about, so the decision happens before the charge rather than after it. Free trials are worth the same treatment on the day you start them.