Autopopulate a field based on 'New' action

Autopopulate a field based on 'New' action

Hello,

I have created a custom module that has a mandatory name field. I need to autopopulate this field with a default value 'BST' whenever the user clicks 'New' to create a new record. The user does not have to enter a value in the name field. It should autopopulate. Please help. 

Thanks,
Imran