What is the best way to go in and apply for jobs?

is it better just to apply online and then walk in with a resume in hand and then request to see the manager or is it better to just do it all in the store?or a cover letter or what? what is the best way in a hiring manager's perspective I'm 17 and im looking to get a job somewhere simple like starbucks or a grocery store or something. im never had a job nor actually applied anywhere