Car Rental, Bangkok
You may try 'tak-taks', the local taxies, they are very cheap. Or you may rent a car, but bear in mind that traffic in Thailand is kept to the left.
At Bangkok airport, as a beginner in global travel n age not on my sight, plane landing at Swarnabhoomi airport was at midnight, Metro trains were closed, little confused, outside it was hot, I ventured with local taxi drivers, shown them d address of my hotels n inquired about d rates, pleasantly bargain was possible n from my indian experience rates were reasonable. they came done from 700 Bahts to 350 Bahts or so. Taxi men was gentle, ride was good. Thai drivers know very little English but things are manageable, they pick commercial practical points n reply as well. people in Thailand are tourist friendly.
Some suggestions for drivers. You can really find a driver anywhere. I would start at your hotel, ask the front desk staff or the concierge for a driver. This may be abit expensive depending on where you'll be staying, but almost all of the hotels will have drivers available, don't be shy about negiotiating a price whether it be at a hotel or anywhere else. TRavel agents may be able to set you up with a local driver as well, but you'll run into the same issues with a hotel, it may be somewhat expensive. You should have an idea of what you want to see and where you want to go before heading out, leaving enough time in your intinerary to see the sights without rushing through things. Take into account the time of day and weekday v/s weekend for rush hour traffic. There are many guide services that you can hire throghout Bangkok that will have the price of the vehicle included in their rate. This is probably the best way to go and the cheapest. You have a guide, driver, the vehicle all in one inclusive price. This may or may not include meals during the time that you are touring as wel as the tip at the end of the day for each.