The Chao Praya River is a wonderful escape from the noise and pollution of Bangkok. For 20baht you can hop on the Chao Praya Express Tourist boat just behind Kho San Road and take a relaxing ride on the river. Located on Thanon Phra Athit, it is easy to find with a Bangkok map. Make your way to Banglamphu, walk along Kho San Road towards the water and you can’t miss it.
If you really want to save money, you can take the local boat for only 8 baht. It is more crowded and there are no tour guides, but it will get you to where you want to go just fine.
I prefer to take the tourist boat. It is quieter, the seats are comfortable and it doesn’t spew exhaust that chokes you as ride along.
It is an efficient and well-run system.  At each pier the deck hand ties the boat up as he blows his whistle relentlessly to let the captain know what is going on.
A tour guide will talk to you about the sights on the shores and you can sit and listen all the way to its end at the Taksin Bridge where you can grab the sky train back to your original destination.  Make sure to stop and sample some of the many attractions before you leave however, because the boat stops at every major tourist attraction along the river. These sights are some of the most spectacular in the city and a must for every tourist.
You an hop on hop off at China Town, the National Museum, Temple of the Dawn , Wat Arun and Wat Pho.  The Maritime Museum, the Gemstone Market, the Oriental Hotel and of course the Grand Palace, Bangkok’s most popular destination. 
You could spend days in Bangkok and never leave the river.  Every stop is either right on the rivers banks or within walking distance from the Pier.  Why hire an expensive taxi or guide when you can take a scenic river cruise from sight to sight for less than a dollar.
The temples are extraordinary and Wat Pho is a must see destination. The oldest temple in Bangkok, it is home to the 46 meter long reclining Buddha. Lying down, it stands 15 meters high.
Wat Arun aka The Temple of the Dawn is majestic. It stands on the opposite side of the river from the other attractions and its tower stands proudly looking over the water.
Last but not least is the Grand Palace. Built in 1782 it houses the Royal Temple containing the Emerald Buddha. Walk around its beautiful grounds and take in its grandeur.  This is by far the most visited temple in all of Bangkok.
When visiting the wats, make sure to dress properly.  Have respect for the Buddhist culture and follow the guidelines.  In places like the grand Palace, Wat Arun and Wat Pho wear a long sleeved shirt and a sarong or long skirt. Men should wear long pants and have their shoulders covered.
Wear shoes that are easily slipped on and off, as you will need to take your shoes off before entering each temple, but make sure to have closed toes.   You will have to leave your shoes outside at the entrance of each temple so it is best not to wear your favorite Nikes or expensive leather boot’s. Be comfortable and practical.
Once you are done your day of sight seeing, you can hop back on the tourist or local boat and make your way to the Taksin Bridge where you can catch the sky train back to anywhere that you are staying in the city.  Be it Siam Square, or Sukhumvit.  The sky train is quick, efficient, cheap and fast.
Or better yet, hire a tuk tuk to experience a true Thailand tradition. Zip through the streets in a three-wheeler motorcar and feel the energy of the city.  Barter hard however and never fall for the scam of a free or cheap 10 baht ride because they will take you to every tourist trap and gem market until you buy something.  Once they have their commission, you may not have a lift back to your hotel.
With a good map, a guide book and a firm resolve to stick to your plans, getting around Bangkok can be a lot of fun and a few days by the river can be a rejuvenating experience.