If your vehicle is a TOTAL Loss.
Do your homework. Check for similar vehicles in the local papers, Bargain finders, Auto Traders. Keep in mind that these values are usually a laypersons opinion of value (Market Value) Also call dealers and look for vehicles similar to yours a year newer or a year older is fine too.
Locate and make copies of all your maintenance invoices. Items like tires, battery, exhaust, shocks, mechanical and breaks etc do add to the overall value of the vehicle.
NOTE! They do not add the total value of what you spent, but they do increase the value by a percentage.