For Common scenarios for Apex Trigger in Salesforce, check the following

1. How to avoid closing Parent Case when child(related) cases are still open in Salesforce?

 

2. How to update parent records when task is created or updated?

 

3. Trigger to find Case assigned date and time in Salesforce

https://www.infallibletechie.com/2015/05/trigger-to-find-case-assigned-date-and.html  

4. How to update child records when parent record is updated in Salesforce?

 

5. How to track more than 20 fields values in Salesforce?

 

6. Trigger to send a pdf along with email in Salesforce

https://www.infallibletechie.com/2013/07/trigger-to-send-pdf-along-with-email-in.html  

7. Trigger to capture Deactivation of User date

 

8. Trigger to count number of Contacts associated with an Account

 

9. Trigger to store case’s previous status in Salesforce  

 

10. Trigger to restrict attachment Size restriction in Salesforce

https://www.infallibletechie.com/2015/01/trigger-to-restrict-attachment-size.html