It's ShirleyV you need to speak to. I'll text her for you.

Chao Praya River and some of the canals on Thon Buri side. Easy enough just to tuk tuk along to river and pick up a boat from there. Be prepared to get best price though..and always ascertain price of tuk tuk BEFORE getting in it.

Floating market is good too as is a wander through Chinatown.

Wat Po with the reclining buddha IMO is a must...as is Grand Palace. Also a trip down the Khao San Road - and now the road running parallel with this is also great now for eating/drinking (same road that the Vieng Thai Hotel is in)

How long are you staying in Bangkok for?? It's great using the water taxis...but be prepared to jump on and off them quick lol! For a lovely view over the river and cocktails River View Guest House is lovely!

I'm jealous! Not going to Thailand this year.
http://www.chaophrayaexpressboat.com/en/tourist/
This is your best bet for your first day of siteseeing. Most of the major sites are accessible this way. The tourist boat ticket is for a day so its hop on/off. At the end of the day you will know what you still have to see- then either buy a further day on the tourist boat or be adventurous
http://www.chaophrayaexpressboat.com/en/services/
The express services are exactly what they say. They can be a bit of an adventure- especially if you go for the cheapest one! They have different stops so you need to check before boarding.

Bangkok can seem a bit overwhelming at first. It's easy and cheap to do yourself though, using a mix of the Skytrain, Underground and River express boats. However most hotels will have a tour desk where you could setup a tour at reasonably short notice should you feel thats the route you might want to take on a first visit. Take a look at the websites of Diethelm Travel and Tour East for an idea of the tours available. If you're travelling through an operator then they will make tours available.

Beware of people telling you the attraction you're going to visit is closed (places like Grand Palace, Jim Thomsons House) - it's most likely they're open. Personally we avoid Tuk Tuks now as we've had a couple of instances of being dropped off in the middle of nowhere even though destination and price had been negotiated before getting in - the reason, because we refused the diversion to the gem factory outlet.

I agree with Sunbear that Bangkok can be a bit overwhelming on the first visit, particularly if you are jetlagged. And for anyone else thinking of Bangkok on the way to a beach resort, think about doing the city AFTER the resort- when you are more with it.
We did do a guided tour on our first ever day so that is definitely an option to make it easier. However, we did end up at a gem factory so be aware of that. With the tourist boat, you won't have to worry about gem factories

Yes that happened to us once, but we were stopped by man on the street when we were foolishly looking at a map! LOL he told us that the Temple of Dawn was shut but to go to another temple - he duly stopped a tuk tuk driver, spoke in Thai and said he'd take us. Luckily there were four of us on this holiday - and we were taken to a small temple where a booted and suited Thai man waiting outside started talking to us. We then realised it was a scam to get us to - the tuk tuk driver refused to take us back - so we walked.

I was just crossing the road this year in Bangkok and elderly thai man next to me told me Grand Palace was shut I just laughed and carried on walking.

I've been told the Grand Palace was shut as well. Funnily enough, one year it was actually shut for the day and I was imagining these poor Thais telling the truth and no-one believing them

Vimanmek Palace is a must see sight. And there is this aquarium called Siam Ocean World, the largest one in Southeast asia! Then there is Chinatown Bangkok and the safari world that you mustn't miss out on. Hope you have a great trip

Have a drink in the Skybar. Expensive but worth it.

I am scared of heights but still glad I went even though my legs gave way when I looked over the edge