I was in Thailand for three weeks last month, travelling with seven friends. We had a simply wonderful time.
Four hot, sweaty days in BKK.
I cannot reiterate enough what other posters have said; BMK food court is great! WE ate our first meal there, and it was a great opener. No matter how ready you think you are to hit the streets and start chowing, Bangkok will intimidate the hell out of you, and the food court has stall after stall in a concentrated area. My boyfriend insists the pad thai he had here was the best of our trip; the ingredients were very fresh and the ratio of bean sprouts to noodles was spot on. Also in the food court was a teppenyaki resto (Japanese BBQ). Lovely food we had prawn noodles, cubed steak and fried enoki mushrooms and asparagus. So quick and fresh its the first time Ive had enoki cooked. They were steamed and then grilled with garlic butter. Mmmm
If you go to the World Trade Centre, look out for the guy selling waffle fish on the street out front. Lovely little waffle fish stuffed with things like red bean paste.
Chinatown was wonderful busy, crowded, everything a Chinatown should be. Had lovely roasted chestnuts off the side of the street. Lots of fun!
Just outside of BKK:
We spent two nights on the River Kwai Jungle Rafts, about three hours north of BKK. It was lovely you spend the day in a tour bus stopping at historic sites on the way, and then can do additional tours/activities from the Jungle Rafts. The Rafts are actually rustic rooms with en suite bathrooms floating on rafts moored to the riverbank. Its a very simple set up, but beautiful (imagine reed-woven walls, hammocks, balconies overlooking the river and potplants in every nook and cranny). The food was great, too. Lunch and dinner were set meals (theres a European option, but I didnt see anyone choose it whilst we were there). Usually three or four traditional thai dishes with plenty of rice. We did it first thing upon arriving in Thailand, and it was a great way to sample different Thai dishes, get an idea of the range of flavours and meats, etc. Horrible hearty American breakfast, but it was worth it for the lunches and dinners. The floating massage parlour was lovely, too!
We had lots of fun riding the tuk-tuks, until we got totally screwed over by a seemingly nice driver. Never ever tell a tuk-tuk driver you are going to a restaurant. We told one the address we had given him was that of a seafood restaurant; of course, we ended up on the other side of town at his uncles seafood restaurant. Either refuse to divulge that your destination is a restaurant, or say very firmly that you are meeting friends there. Taxis are a better bet (cheaper, safer) than tuk-tuks anyway, as long as you insist that the driver turns on the meter.
If youre travelling across country, try a night train. Second class air conditioning gives you curtained-off bunks, and first a/c gives you a private room for two, also with bunks. We had immense fun travelling from place to place like this. We usually didnt buy the set meals onboard (pretty good quality, actually) but rather bought from vendors at stations we stopped at.
If you go to the Grand Palace, go early in the morning (it gets very full very fast), and remember that your shoes must have a back to them (i.e. no slides, slip slops) and men will need full length pants, and women skirts that cover your thighs. Everyone should cover their shoulders. They are very strict about this!
MBK and Puntip Plaza are exhausting shopping centres. I recommend doing as much shopping in other parts of the country (Chiang Mai! Chiang Mai!) and then coming here to tie up loose ends, etc. You can never see it all, so dont even try!
The TAT (Tourism Authority of Thailand), located by the main train station, was very helpful they booked tickets, tours, etc. for us. However, the TATs in Samui and Chiang Mai were useless, so it really must depend on what branch you visit.