Always provide the hijacked Steam account's login name in your first message to Steam Support.
Attach as much proof of ownership for this account as you can.
Categorize your ticket in the "Account Questions" category and "Hijacked or stolen account" subcategory.
If you are able to restore access to your Steam account and your ticket is still open, log in to your Steam Support account and close your ticket.
Failure to provide all necessary information when submitting a ticket can only cause a longer delay before your issue is resolved.