How to make all fields mandatory in sales order T- code VA11 initial screen and line item

Dear All,

How to make Sales Office field mandatory in VA11 initial screen? I mean in the first screen where we enter the document type and the sales area?

The fields are

Sales Organization

Distribution Channel

Division

Sales Office

Sales Group

And i want to set a mandatory field storage location also in line item it is possible ??? give me idea step by step how to do it.

Regards,

Richa