Set a default Lead Source on Estimates

1. Navigate to Customization > Workflow > Workflows > New
2. Set the following:

• Name: (Enter a Name for your Workflow For example, "Set Default Lead Source for Estimates")
• Record Type: Transaction
• Sub Types: Estimate
• Execute as Admin is checked
• Release Status: Released
• Event Based: On Create
• Trigger Type: All

3. Click Save.
4. Click New State.
5. Enter a Name then click Save.
6. Click the New State.
7. Click on New Action.
8. Choose Set Field Value for the Type.
9. Set Trigger On = Entry.
10. In the Parameters section, set Field = Lead Source. 
11. In the Value section, mark Static Value and select the default Lead Source value in the Selection field.
12. Click Save.