Take the BTS Skytrain in Bangkok
It's no problem sightseeing in Bangkok, with their BTS Skytrain you can travel arround the city and explore on your own. It's easy and there are staff to help you if u loose your way. Here you can see maps of BTS Skytrain and how to get easy acces to Skytrain.
If you want to take more than just 2-3 trips with BTS Skytrain, then go buy a rabbit card. It's a creditcard size card you can put money into and travel easy. After buying a rabbit card you do not have to wait for tickets anymore. You simply hold your rabbit card over then entrance machine and then you are ready to go. You will also recive special offers by using the rabbit card
The Skytrain system in Bangkok is a great way to see the city. You can also take the MRT, this is the underground metro, click here to learn more.
Video from the BTS station National stadium