Best Practice for making fields mandatory

The best practice for making certain fields mandatory is to set the fields as fields on the page layout:

1. Navigate to Setup and search for Object Manager.
2. Select the object where you want to set required fields. 
3. Click Page Layouts. 
4. Select the field you want to set as required.
5. Click on the Properties (wrench) icon.
6. Select the Required checkbox.
7. Click Ok.
8. Save your changes.

Note: You will need to update the layout of all relevant record types if numerous record types exist.