The Monkeys have both been to Thailand and visited many of the same attractions ( I guess most tourists have) but not at the same time, and also for different purposes.
One Monkeyme went for immigration purposes while Second Monkeyme was worked related. Between us, we have visited an elephant Sanctuary, the Golden Buddha Temple, River Kwai Bridge, Floating Market, and the refugee settlement areas - me for sightseeing, Second Monkeyme for educational purposes.
The Grand Palace
I have been to Krabi, Phuket, Ko Phi Phi, Ko Phangan, Chiang Rai, and Chang Khiong. My favorite place to stay in Bangkok was at Khao San Road - it is not only where all the cheap guesthouses are located , but it is also colorful and has everything you want from all the things going on there - you can hop on a bus right in front of your guesthouse to go anywhere. I also liked seeing all the crazy tourists from all over the world with their antics and vibes. People-watching can be somewhat entertaining too. They are all over Khao San Road.
Khao San Restaurant
I usually start my Thailand trips from Penang, and sometimes, if I don't have much time, directly from Kuala Lumpur. I always take the overnight bus. This way, you'll save on your hotel bills, as you can sleep in the bus - for some people it is uncomfortable but for the Monkeys, no worries.
Depending on your interests, Thailand is not called "Land of Smiles" for no reason. If you're a water person, the South is for you - it has nice beaches, good diving spots, and every water activity you can think of. Head North if you are interested in mountains, tribes, rivers, and wildlife. I have a soft spot for Bangkok and Ko-Phangan; I have taken 2 thai massage classes in Bangkok and in Ko Phangan I helped one of the owners serve the "Farang" during one of the Full Moon parties at her small space on Hadren Beach, as I speak English pretty well. (I didn't get paid for my help but was offered free accommodation and food.)
Chao Phraya River King Rama VIII Bridge at Night
The Full Moon party is non-stop music, dancing, and drinking. There are cases of people drowning, so it is a good idea to stay within your boundaries and avoid excessiveness. Some dodgy characters are also around, pretending to be tourists. When I was there, I had many offers for drugs, presumably to give you more energy and a great time - you just have to politely decline.
Ko-Phangan is a nice island with friendly people. Though I've seen nicer beaches in other places, the full moon party is popular and for some tourists, the only reason to visit the island. In reality, there are other beaches that are more for family visits on the island. The Sanctuary is quiet and has a family atmosphere at Hat Thian's beach. I stayed there for 2 days, just to relax after my Full Moon stint. They have some yoga going on and the owner's arrange dinner for all the guest at the beach. So you can actually meet other people .
Soi Ram Butri, Khao San
Ko Phangan is highly worth visiting even if the "Full Moon" party is not your cup of tea. The town Thong Sala has a laid back atmosphere and cheap food and accommodations.
Crowds at The Grand Palace