Contrary to advice given in many Bangkok travel guides to avoid using tuk-tuks in Bangkok I am going to recommend you use them for short journeys of only a few miles. They are fun. I thoroughly enjoyed travelling on this unusual form of transport with built in natural air-conditioning.
There are no windows at the sides or back just a roof. There is a bench seat in the rear. They were designed for the local population to use. Not giant westerners. If you are 6 foot or over you will have a problem. Your head will be stuck inside the roof of the Tuk-tuk and you will not be able to see out. I am over 6 foot and found that I had to practically lie down in the back and hold onto the rails to be able to see out.
I found you could take some great photographs from inside a tuk-tuk. The local Thais do not notice you taking photos so it allows you to take some great candid shoots. Make sure you use the telephoto lens and set your camera aperture control to the sport setting as you need a fast shutter speed because you are in a moving vehicle.
The tuk-tuk is named after the sound of their engine, they are motorized rickshaws. You MUST arrange the price with the tuk-tuk driver before you get in. Ask at the Hotel reception desk how much a Tuk-tuk should charge for where you want to go so you have an idea of the correct rate. Tell the Tuk-tuk driver where you want to go and he will normally double the standard rate he charges local Thais because you are a tourist.
In this example my Hotel told me that it should cost 100 Baht. 'I want to go to the Grand Palace. How Much?' Driver responds, '200 Baht'. You reply 'No No that is too much it is a 50 Baht trip' He will Reply '150 Baht' You counter bid, 'I will give you 100 Baht no more.' If he refuses to meet your price walk away towards the next tuk-tuk in the taxi rank.
He will normally come after you, 'Okay okay 100 Baht.' I got in the habit of having a pen and paper handy and writing the agreed price down and then showing it to the driver. '100 Baht yes?' and the driver confirms '100 Baht yes'. This stops the tuk-tuk driver demanding a ridiculous fare when you arrive at your destination resulting in an unpleasant situation.
A lot of the Tuk-tuk drivers have only a few words of English. What I found very useful was to point to the place you wanted to go to on a map that has place names in English and Thai. Your hotel will normally give you such a map free of charge. As they are thinner than a taxi they are great at weaving in and out of Bangkok's heavy traffic and can sometimes get you there quicker. Do not to rest your feet on the rail near the drivers head, as doing so is extremely disrespectful towards the driver. Showing someone the soles of your feet or shoes is considered rude in Thailand.
Tuk-tuks are just motorbikes on steroids. Like any motorbike in a city, drivers and passengers are exposed to vehicle pollution and offer almost no protection in case of an accident. Tuk-tuks have water proof removable sides that can be added in the rainy season. If you find a tuk-tuk driver with good English you may want to consider using hiring him for the morning or whole day.
We managed to do this on my last trip. We had seen all the main sights and I told him the sort of things we were interested in seeing. He took us to some great lesser known temples, markets and tourist sights. I had some specific clothes I wanted to buy so he took me to the right wholesale outlets so I could get a good deal.