Trigger Order of Execution

1. System Validation rule (required field, field format) (SV)
2. Before Triggers are executed (BT)
3. Custom Validation rules are checked (CV)
4. After Triggers are executed (AT)
5. Assignment Rules are executed (AR)
6. Auto-Response Rules are executed (ARR)
7. Workflow Rules are executed (WR)
   1. Before and after triggers are executed one more time if the workflow rule updates a field (BT & AT)
8. Escalation Rules are executed (ER)
9. Parent Rollup Summary Formula or Cross Object Formula fields are updated in the respective objects. (RSF, COF) (These parent records also goes through the entire execution order)
10. Criteria Based Sharing rules are evaluated (CBS)
11. Any Post-Commit Logic is executed (PCL)  (like sending an email)

To remember this sequence you can memorise the following.

SV -> BT -> CV -> AT -> AR -> ARR -> WR (BT, AT) -> ER -> RSFCOF -> CBS -> PCL