I have several simple rules:
1. Track it - Google Sheets, apps, counters, etc.
2. Don’t make excuses - easier said than done. But really, only outlier reasons should trip you up.
3. You won’t go from 0-100 at once - Routines are sometimes set with expectation that something will be complete or expert or entirely satisfactory but time is also important. Your routine doesn’t need to be perfect!
4. Bonus - try to do things at the same time on whatever recurring interval you use. I go to the gym every morning within the same 10 minute window. If not, the chances of not going skyrockets (see 2)