By bus
This first tip on bus travel is one to remember: do not do it! Sukhumvit Road is probably the most congested road of Bangkok and traffic jams exist the whole day until late in the evening. Also, it is difficult to find out which bus goes where or where to get out. Better take the Skytrain, metro or express boat, even if it costs a little more.
If you insist, there are many bus routes through the Sukhumvit area. The most important one is ordinary and air-conditioned bus 25, which starts far southeast of Sukhumvit Road. From there, it goes all the way northwest along Sukhumvit Road and then rides over Ratchadamri Road and Rama IV Road to Silom. It then continues its way to Hualamphong Train Station, through either Charoen Krung Road or Yaowarat Road depending on direction and finally on to Tha Chang in Rattanakosin for the Grand Palace.
From the new Suvarnabhumi Airport, you can take bus AE3 for 150 baht to Sukhumvit. It runs up the Bang Na-Trat Expressway and along Sukhumvit all the way up to Siam Square. It then loops back around to Nana and then back out to the airport. Another option is bus 552, which heads on to On Nut, where you can continue your way with the Skytrain. There are many stops and depending on traffic the ride can take from 1 to 2 hours.
By ship
The Saen Saep Express Boat service is a rough, but entertaining way of getting in and around Sukhumvit. The Saen Saeb canal forms the northern boundary of Sukhumvit's sois and is a cheap alternative means of escaping the traffic jams if you're coming from Khao San Road, the eastern side of Rattanakosin or Ramkhamhaeng.
There are two lines: The Golden Mount Line runs from Panfa Leelard near the Golden Mount in Rattanakosin east to Pratunam near Ratchaprasong intersection. The NIDA Line runs from Pratunam all the way northeast along Ramkhamhaeng Road to Wat Sriboonreung. A single trip from Panfa Leelard to Nana Nua takes about 35 minutes and costs 13 baht. You must switch boats at Pratunam. Other stops along Sukhumvit's northern sois from west to east are Nana Chard, Asoke-Petchaburi, Prasanmit, Italthai, Wat Mai Chonglom, Baan Don Mosque, Soi Thonglor, Charn Issara and Vijit School.
If you're coming from the Grand Palace area in Rattanakosin, there are two ways to get into Sukhumvit. The fastest way is to take the Chao Phraya Express Boat to Sathorn pier in Silom. From there, continue your way north using the BTS Skytrain Silom Line. You'll need to switch trains at Siam BTS station and continue your way east onto the Sukhumvit Line. The whole ride from Rattanakosin takes about 40 minutes. You can also choose to take the 30-minutes walk or a five minutes taxi ride to Panfa Leelard pier and continue your journey using the Saen Saep Express Boat.