You can drive in Guatemala with your home-country driver's license or with an International Driving Permit (IDP). Guatemalan driving etiquette will probably be very different from what you're used to back home: passing on blind curves, ceding the right of way to vehicles coming uphill on narrow passes and deafening honking for no apparent reason are just the start. Expect few road signs and no indication from other drivers of what they are about to do. Do not pay any attention to turn signals – they are rarely used and even more rarely used to indicate a turn in the direction they would seem to be. Hazard lights generally mean that the driver is about to do something foolish and/or illegal.
A vehicle coming uphill always has the right of way. Túmulos are speed bumps that are generously (sometimes oddly) placed throughout the country, usually on the main drag through a town. Use of seat belts is obligatory, but generally not practiced.
Navigating colonial-era street plans, which often control traffic with devilish one-way systems, can be a nightmare.
In Guatemala driving at night is a bad idea for many reasons, not the least of which are armed bandits, drunk drivers and decreased visibility.
Every driver involved in an accident that results in injury or death is taken into custody until a judge determines responsibility.
If someone's car breaks down on the highway (particularly on curvy mountain roads), they'll warn other drivers by putting shrubs or small branches on the road for a few hundred meters beforehand. Annoyingly, they rarely pick them up afterwards but if you're driving and you see these, it's best to be cautious and slow down.
While car hire is certainly possible, if you're sticking to the main sights, logistically it is rarely a good idea – Antigua is best seen on foot, the villages around Lago de Atitlán are best visited by boat, and the distance from either of those to Tikal makes it a much better idea to catch a bus or fly. That said, for freedom and comfort, nothing beats having your own wheels.
There are car-hire places in all the major tourist cities. To rent a car or motorcycle you need to show your passport, driver's license and a major credit card. Usually, the person renting the vehicle must be 25 years or older. Insurance policies accompanying rental cars may not protect you from loss or theft, in which case you could be liable for hundreds or even thousands of dollars in damages. Be careful where you park, especially in Guatemala City and at night. Even if your hotel does not have parking, they will know of a secure garage somewhere nearby. Red-painted kerbs mean no parking.
Motorcycles are available for rent in Antigua and around Lago de Atitlán. Bringing safety gear is highly recommended.