When you need hotel recommendations always mention how much per night you want to pay for that room. This will narrow down the choices you get because a price range for a hotel with air and private toilet will run from around 600 baht to 6000 per night.
My recommendation is to get a hotel near the Skytrain route. That way you can use that overhead transportation for getting around town quick and easy. If you are a kid or real young perhaps staying in the Khao San Road area will be okay. No Skytrain stop though!
http://www.khaosanroad.com/
I prefer the Sukhumvit/Siam area where you have hotels in various price ranges and close to the Skytrain.
http://www.thaiwebsites.com/hotels-sukhu…
Here is a hotel that is close enough to the Skytrain so you can walk. Close to malls, street vendors, bars, restaurants and travel agencies for tours.
Ibis Nana Hotel:
http://www.bangkok.com/ibis-nana/
Here are some travel forums you can look over for help and specific questions. Pay particular attention to transportation from the airport, using meter taxi cabs and some of the scams you may encounter.
http://www.tripadvisor.com/ShowForum-g29…
http://www.lonelyplanet.com/thorntree/in…
Don't waste all of your time only at beaches. Even in Bangkok and Chiang Mai you can get a tan just walking around.
Good luck.