Upon arrival at the rental desk: Remember to produce all documents required and inform the rental clerk of any additional driver's and any extra's that you may have booked. Remember to read fully the rental agreement and make sure that you fully understand all the insurance details before you leave. Check for any damage to the rental vehicle and take photos as appropriate and inform the rental clerk of any damage found BEFORE you take posession of the vehicle. Ensure that you have any extra's that you requested and have planned your route, enquire about a map if needed.
Returning the rental vehicle: Check for any damage, take photos and inform the rental clerk if needed. Ensure the rental agent signs off the drop off. Make sure you have taken all your belongings with you.
Useful advice: It may seem obvious to us all, but the more we know about the location we are going to, the more prepared we will be! it is therefore a good idea to try and research as much as you can about the location you are going to BEFORE you travel to better prepare yourself upon arrival, knowing things like the rules of the road, local do's and don'ts, attractions to visit, planning your routes beforehand if possible, having a torch handy, a phrase book on the language, and all your documents needed close to hand, with photocopies of your passport (so you don't have to carry round the original with you all the time), having a cellphone are just some of the things that maybe of use to some of you when renting a vehicle.