You might have a roommate or family member on your policy that no longer drives your vehicles. Or maybe you have a vehicle on your policy that is no longer being driven. Making sure driver and vehicle information is up to date may save you money. Keep in mind, if you do go down to just one car on your policy, you will lose the multi-vehicle discount.
The cheapest car insurance, period, will likely carry the minimum coverage required in your state. In most states, this is liability insurance only, which covers property damage and medical bills for others due to accidents you cause. Some states also require uninsured and underinsured motorist coverage, which pay for your injuries or damage if an at-fault driver doesn’t have enough insurance.
But liability coverage levels come in threes — you’ll probably see something like 50/100/50 up to 250/500/250 in typical policies. You can think of these limits like: individual injuries / total injuries / property damage. Insurers are a little more technical, calling them bodily injury liability, total bodily injury liability and physical damage liability.
Teenage drivers who have no driving record will have higher car insurance premiums. However, young drivers are often offered discounts if they undertake further driver training on recognized courses, such as the Pass Plus scheme in the UK. In the US many insurers offer a good-grade discount to students with a good academic record and resident-student discounts to those who live away from home. Generally insurance premiums tend to become lower at the age of 25. Some insurance companies offer "stand alone" car insurance policies specifically for teenagers with lower premiums. By placing restrictions on teenagers' driving (forbidding driving after dark, or giving rides to other teens, for example), these companies effectively reduce their risk.
Providers can also offer sub-divisions of auto repair insurance. There is standard repair insurance which covers the wear and tear of vehicles, and naturally occurring breakdowns. Some companies will only offer mechanical breakdown insurance, which only covers repairs necessary when breakable parts need to be fixed or replaced. These parts include transmissions, oil pumps, pistons, timing gears, flywheels, valves, axles and joints. 
In September 2012, it was announced that the Competition Commission had launched an investigation into the UK system for credit repairs and credit hire of an alternative vehicle leading to claims from third parties following an accident. Where their client is considered to be not at fault, Accident Management Companies will take over the running of their client's claim and arrange everything for them, usually on a 'No Win - No Fee' basis. It was shown that the insurers of the at-fault vehicle, were unable to intervene in order to have control over the costs that were applied to the claim by means of repairs, storage, vehicle hire, referral fees and personal injury. The subsequent cost of some items submitted for consideration has been a cause for concern over recent years as this has caused an increase in the premium costs, contrary to the general duty of all involved to mitigate the cost of claims. Also, the recent craze of "Cash for crash" has substantially raised the cost of policies. This is where two parties arrange a collision between their vehicles and one driver making excessive claims for damage and non-existent injuries to themselves and the passengers that they had arranged to be "in the vehicle" at the time of the collision. Another recent development has seen crashes being caused deliberately by a driver "slamming" on their brakes so that the driver behind hits them, this is usually carried out at roundabouts, when the following driver is looking to the right for oncoming traffic and does not notice that the vehicle in front has suddenly stopped for no reason. The 'staging' of a motor collision on the Public Highway for the purpose of attempting an insurance fraud is considered by the Courts to be organised crime and upon conviction is dealt with as such.
Auto insurance is financial protection, and not just for the investment you made when you bought your car. After a really serious accident, bills for damage and injuries can easily reach into hundreds of thousands of dollars. If you happen to cause such a wreck, the victims could sue you. In the worst case scenario, assets such as your savings and home could be seized.