From some very recent experience, here's a few things to look for, consider, and address with your insurance company.
1. As stated earlier, the insurance co will have a 3rd party do the valuation of your vehicle. Review this valuation carefully for accuracy (more on that below)
2. Overall, if you are not happy with the valuation and settlement, tell them so and do not cash their check. The valuation and settlement amount is completely negotiable, so continue to work with them to get to a number you a happy with. Best to back it up with facts/data. Number 1 thing to remember is that they have to put you in an equivalent financial position as to prior to the accident, less your deductible.
3. The valuation will utilize comparison vehicles from the local area that are either currently advertised or 30 days old. Sometimes this makes it difficult to verify that these comparison vehicles are actually a good comparison.
4. Make sure the valuation captures ALL of the options that your vehicle had (ACCURACY FLAG). Best way to verify this is to call any dealership and ask for the build sheet for your vehicle. They will take your VIN# and print it right away. You would think the 3rd party would do similar, but they don't.
5. Make sure the valuation captures the right type of model of your vehicle (ACCURACY FLAG). You don't want them calling it an SR5 type when it was a Sport or Limited. Tough to get this wrong, but they do!
6. Make sure any after market additions to the vehicle are accounted for (ACCURACY FLAG). The 3rd party will not even look at this stuff - you have to take the initiative. Sometimes the Insurance Co will ask for receipts to those (like who keeps those), but sometimes pictures of the actual vehicle and weblinks to buying new components will suffice. Be prepared for the Insurance Co to depreciate those after market mods, of which is also negotiable.
7. A tough one to address is the actual mileage vs. the mileage of the comparison vehicles. Based on the comps, they will adjust up or down. Its hard to know their formula for doing this, so do the best you can to approximate whether the adjustment makes sense to your vehicle (ACCURACY FLAG). Here again, another area open for negotiation if it doesn't make sense to you.
8. Lastly, the toughest one to deal with is something called "baseline adjustment". IMO, this is where they make their money off you. Baseline adjustment means they will adjust the value of your vehicle DOWN. This is because it is being driven on a daily basis and therefore WORTH LESS than an equivalent vehicle that is sitting on a dealer lot all shiny and clean.
9. When negotiating, the Insurance Adjuster you work with will have some flexibility to change the valuation, but not a lot. Be cognizant there is a threshold where they need to get higher mgmt approval. (which sometimes pisses the adjuster off since they're operating on a scorecard as to how well they close claims and how close the come to the original valuation).
Hopefully this info helps you get a fair deal for your vehicle.