Driving abroad can be stressful. Making sure the map is not upside down and decoding multilingual road signs is difficult enough, but before you even get into second gear, there is the small matter of hiring a car to worry about.

"There are people who arrive through customs and head straight for the car-rental desks. They come in once and find they can get a cheaper deal by doing that but when they try it again, they find there's no cars left or it's more expensive than if they had booked in advance. It's all supply and demand," says Mr Aidan Lenihan, sales and marketing manager for Budget Rent a Car.

Book in advance and book online is the advice most agencies give to people looking for the cheapest car-rental rates. "I would say check the Web constantly, because that's where you will find deals without the commission, without the middle- man," says Ms Niamh Colgan, sales and marketing manager for Murrays Europcar.

"People should also be aware that car-rental deals advertised on airline websites might not be as cheap as offers available on the car-rental site itself, because of marketing fees and airport surcharges," she says.

Booking online is the top tip for renting a car from a top 10 list compiled by Argus Car Rentals.

"Car rentals that are online work on the same system as online airlines," says Mr Greg Turley, managing director of Argus. For example, Argus has advertised an advance special offer of €199 for a car for seven days in July; the normal price could be €250 or €299, depending on the type of car.

Booking in advance means that people who want to rent a car can get a full explanation of the different types of optional insurance available and don't have to make a snap decision, according to Mr Dermot Carberry, sales and marketing manager for Avis Rent a Car.

With all car rentals, basic third-party insurance is legally required and is usually included in the price.

The majority of agencies will also provide collision damage waiver (CDW) and loss damage waiver (LDW) at extra cost, clearing the client for most of the liability.

Most companies will still hold the client liable for a proportion of any damage, for example the first €400. This "excess" amount can vary between €300 and €1,000, so it is in the client's interest to check these insurance conditions at the time of rental.

If you intend to rent a car on holiday, bring your driving licence and credit card with you on collection of your car. Book your infant or child seat well in advance as most car companies have a limited supply. Always return your car full of petrol.

Argus advises holiday-makers to check for additional charges, such as "one-way rental" charges if you are returning your car to a different location than where you hired it.

"This will vary by kilometre, so there wouldn't be a huge charge in Ireland, but in Europe if you plan to leave the car in another country or region than where you hired it, you need to know how much extra this will cost," says Mr Turley.

Finally, you should always inspect the car on hire so you will not be charged for any dents or marks you haven't made during the pick-up inspection. Some agencies will give clients a picture of the car, with any existing marks identified.

"Like everything else, it's purchaser beware," says Mr Turley. "Don't just jump into the car and drive."