What part of Thailand?
When I went 2 years ago, we stayed in Bangkok for 2 nights, 2 nights in Koh Samoi, and 2 nights in Phuket.
Bangkok - book a tour that will take you to different temples. I think we did one where we saw like 4 or 5 temples in 1 day. At night goto local night markets. Some night markets are know as a red light district, some are known for shopping for cheap items, some have better music/social atmosphere.. depends on what your into. So much to do in Bangkok as it is a metro area. Be prepared for humid, smog, and traffic.
Good food is everywhere. People are generally nice, but of course be aware of scammers if you look like a tourist. Ooh yea, we had my birthday dinner at a high rise rooftop restaurant. Wait, we actually stayed at the same hotel. Lol... we stayed at Banyan tree hotel and their rooftop restaurant/bar is called vertigo and moon bar.
Koh Samoi - small island, did a lot of R&R.. chillen by the pool and beach. Took a tuk tuk to their local bar/restaurant area.. but very nice and relaxing island. Oh, we went ATV riding here through the jungle.. it was pretty fun. We stayed at Privelege hotel, the swimming pool was 10 feet away from the beach lol.
Phuket- bigger island, we stayed at Keemala, treehouse hotel/suites in the jungle. Totally fun experience. You should check it out if your going to this island. Our room had a private pool and was pretty secluded, so we m just stayed and basked in the natural beauty for 1 day. We booked a private driver through the hotel another day that drove us all over the island. We went to tiger kingdom and got to pet tigers, drove up to see big Buddha, fed wild monkeys at a park, and a bunch of other tourist stops.