Wht to do if I was a passenger in a car accident where the other driver was at fault?

There are two things that you need to do, in general.  The first is to contact both insurance companies to assert a claim.  The second thing you need to do is consult with a personal injury attorney to help you with your case.  I strongly suggest visiting with at least three so that you find an attorney that understands you and your needs.

As far as settlement, if the driver of the car was not at fault, then more than likely his insurance is not going to pay.  If there was some negligence by both drivers, then both may have to pay a certain percentage of the overall settlement.  If the other driver is primarily responsible-- then their company will most likely be paying the bulk of the claim.  The reason you want to contact both companies is in the event that one company fingerpoints at the other company-- filing a claim with both covers you basis-- the main thing is that one or both cover your expenses

The amount of your settlement will depend on the extent of your injuries.  If you have permanent injuries, you can expect a higher settlement.  If you have injuries that can be resolved with treatment, then you will receive a medium settlement.  If you only experienced pain and the injuries can resolve themselves with little medical attention, you will receive a nominal settlement.  You can also receive compensation for lost wages.  This is a rough guideline-- but it gives you an idea of how the settlements are increased.  To have a more specific idea of the exact value of your case, take copies of whatever medical records you have, the traffic/offense report, and your latest W-2 to a personal injury attorney.  Many will provide free consultations, especially if you have done much of the pre-work for them.