Air conditioning is a safety feature. If you are driving with your windows open, you are inviting local thieves to help themselves to your valuables every time you stop (or even just slow) the car. If you are traveling in a warm climate with sick or elderly people, air conditioning becomes increasingly important.

To make securing your car easier, consider renting a car with power windows and universal door locks. If you know you will be driving through high-crime neighborhoods, or will be parking the car in unsafe lots, rent a car with a good security system. 

Are there any stickers, license holders or other markings that tell the world you're driving a rental car? This may attract the attention of thieves or terrorists. When you make your reservation, ask for a car without such markings.

When you get inside the car, take five minutes to orient yourself. Learn the location of the headlights, brights, windshield wipers, defroster, horn, etc. Adjust the mirrors. Is the gas tank full? Do a quick inspection of the car. 

It's a good idea to spot any defects before a local law enforcement officer does. If you notice any problems with the car (especially scratches or dents) let the rental agent know before you take the car off the lot, or they could hold you responsible for the damage. On the rental contract, write down the auto's make, model, color and license number. Keep the carbon copy of the contract with you. If the car is stolen, you'll want to have the information handy. 

Always drive with the windows up and the doors locked at all times. Always wear your seat belt. When it is raining, regardless of the time of day or the amount of light, you should put on your low beam headlights. This makes it easier for other cars to see you. In some U.S. states, like Florida, it is the law. Because you won't know the local laws, it is better to err on the side of safety.

Beware of slippery roads if it hasn't rained for a while. When it rains, oil that has soaked into the concrete rises to the surface and makes the road very slippery. Give yourself an extra margin of error when driving. Try to have at least four seconds of stopping distance between you and the car in front of you.

If you are traveling in the United States and have a cell phone, double check with your provider that you have national coverage. (If you don't, get it.) 

Avoid driving at night. Park in a well lit area, with security cameras, if possible. Usually, the car rental agent can tell you which parts of town to avoid, and if there are any standard scams or attacks to look out for. Ask the rental agent for the local all-news radio station so you can listen to regular traffic reports.