BTS Skytrain: Fast, efficient and affordable, running everyday from 06.00 to midnight.  
Mo Chit station at the north end, where you can find the weekend Chatuchak Market.  

Siam Station, adjacent to huge shopping malls: Siam Centre, Siam Discovery Centre and Siam Paragon, is the central station with a link to National Stadium Station to MBK shopping centre.  Saphan Taksin Station & boat pier. Fares from 10 to 40 baht or 100 baht unlimited day pass.  

Taxi: Very easy to find everywhere in Bangkok, with the meter starting from 35 baht, it's a low cost convenient transport when the traffic is flowing. However, always make sure the driver activate the meter.  Then there is the ubiquitous Tuk tuks touting for business. They’re a fun ‘must-do’ experience but in Bangkok peak traffic the induced fumes are "not fun". If your game try local culture motor bike taxi  say ChaCha (go slow) or ReoReo (go fast)

The river and canal ferry is a whole new must do experience. "Longdo" is Thai for "please try!"

A.P.A.C (Personal Assist <> Concierge)  > Orientation service 

or D.I.Y. google thaibis Public transport Bangkok, here you'll find  
"best tourism stations" linked to venues, Photos, maps, tips and tricks