You'll have a great time in Thailand. Wether it be the madness of Bangkok, the varied islands (I only did a few days on Koh Samui - next time) or somewhere chilled out like Chiang Mai in the north which I really enjoyed.
Great tip with the triple entry elai.
Also for the taxi's I had a few that refused to turn the meter on, say "Meter na khrap", basically please turn on the meter. If several attempts fails make it obvious you want them to pullover and get out. Chances are the next available taxi will pass within a minute.
In bangkok there are a bunch of differnt coloured taxis representing different companies or a loose organisation of private owners, I found the pink ones worked best.
If your having trouble with directions or whatever the drivers have a number they can call that will translate where you are trying to go. They simply call the number, pass the phone to you and you pass it back to the driver who then gets the translated version.
Also if your in a touristy area (anywhere near Khao San Rd for instance) and not in a rush you can get a tuk tuk ride for free. Seriously I was on my last day in Bangkok, just been to Hualamphong station to buy my overnight sleeper ticket to Chiang Mai and was about to catch a cab to head to the big shopping centers of BTK and Siam Paragon when I passed a tuk tuk driver who asked where I was going.
I usually ignored tuk tuk drivers entirelly (they try to take you to the seedy sex shows, typically will way overcharge or take you somewhere completley different where they get a kickback) but I told him and he said 'i take you for free'.
'Just make 1 stop first', I asked what kind of stop, he said he would take me to a good suit store.
I wasntly really interested, but I wasnt in a rush and was intrigued. Sure enough we took maybe a few block detour and pulled up in front of a resonable looking suit store I went in looked around was approached by a salesman who through complete dissinterest I managed to slash his price down to 40% of what he initially offered - I then pushed him more to see just how bargain basement he would go, skimping on a cheaper linning and no internal pockets and things I got him down to almost 15% and then politelty declined stating I was leaving in hours, wouldnt be retuning for a fitting and had no room in my bag.
Tuk tuk driver was waiting for me (with a drink obviously provided by the store), he asked if I had bought anything he said no, I asked if the business would still pay him he said yes he would still get a reward and dropped me at BTK.
I thought I had been lucky though sure enough I repeated the story to a holidaying aid worker on my train and he said he had experienced something very similar a few days ago although he was taken to a souvenir and jewel store.
Learn to bargain and not feel bad about it. You are getting an inflated rate, even when you bargain the price down you are most likely receiving an inflated rate to what the locals get. I took a girl who gave me a haircut in Chiang Mai out one night and was shocked by the prices she paid. Dont get too tight, you are a millionaire compared to them - share the wealth.
Dont get angry, yell and berate them. Thai's will either smile and continue being polite or if you push the issue you will be kicked in the head and you will never see it coming from the cute 4'8" Thai girl. If you were really rude her 4 friends will join in and beat your ass.
I'd book a few days accomodation online before you go, then look for best places and prices on the ground. I stayed at the rather basic
http://penparkplace.com/ clean, good air-con, wifi in rooms, close enough to Khao San that you can walk there, but far enough at the same. Only real complaint was checked in late after or flight and there was a little confusin at first, also there are no nearby skytrain or subway stations, there is a water taxi stop just around the corner however that will take you anywhere along the Chao Phrya River. Also a 7Eleven down the end of the block.
In Chaing Mai I quite liked
http://www.rendezvouscm.com/ and a bit pricer
http://www.parasolinn.com/ both with superbly friendly service.
