For us that don't drive in BKK, knowing all the transportation options sometimes helps you get around faster.
There's the Airport Link, MRT, BTS, Taximeter and Tuk Tuk. Some also take the motosais at the pak sois.
Other not so common modes would be the khlong water taxi (San Saep) which has East and West routes with the interchange at Pratunam.
Another would be the Chao Phraya water boats.
Yet another option are buses. There are songthaews even in BKK. The ones that are somewhat obtuse are the rot tus (vans) that go from point to point e.g. you can take a rot tu that goes from Silom to the Mall Ngamwongwan.
Some of these options have been integrated into Google Maps for at least the last 2 years now.
Here's a pic of a transit option less commonly known to visitors - the State Railway of Thailand (SRT) trains. Pic shows office commuters in the morning taking the train to work.
There sometimes are stations and sometimes it's just a simple stop at the side of the tracks.
You can take the SRT from Don Muang airport, for example, south all the way to Hua Lamphong station.