If you take a taxi, insist that the driver turn on the meter. As we left one of the temples the first taxi driver quoted us a fare of 400 baht (>$12), we walked away and didn't even try to haggle with him. The next several insisted on 200 baht. We finally got one who agreed to use the meter and the fare was 90 baht (<$3). If you work in the States and have money to burn, sure it doesn't seem like much, but it's an unnecessary expense. Agree on a price before taking a motorbike taxi, you can try to haggle it down but good luck. Every time I walk away from one guy who I think wants to charge me too much I end up going with someone else who asks for even more. Regardless, this is my favorite way to travel, you'll get through traffic much quicker, and frankly it's fun. But songthaews (converted pick-up truck taxis) are cheaper and safer. Songthaews generally only go up and down one route, but motorbike taxis will take you just about anywhere.
Thais don't really queue up. I've had more than one person cut in line for the bathroom or in the markets. It's like the lines don't really exist, if there's a spot closer to the target - they're going to hop right in. People pushing shopping carts in the supermarket don't really give way either, I've had to back out of an aisle before because there is just no concept of 'she was already heading this way, I'll let her through before I go'. They just go. Everyone just goes. It's a way of life that is most evident on the streets.
I cannot emphasize this strongly enough - TRAFFIC WILL NOT STOP FOR YOU!!! They might slow down, speed up, or swerve to get around you, but they will NOT stop for you. They won't necessarily stop for red lights either. If you happen to see a rare crosswalk or even rarer crosswalk with a walk/don't walk signal, I promise you, it means nothing. Ok, to be fair, at a cross walk maybe 50% of the cars will actually stop… but that only lulls you into a false sense of security, better to assume that they will not stop. Cars and motorbikes all seem to come out of nowhere. Even after we've cautiously checked both sides of the street before crossing, we've seen parked cars start to back up towards us out of the blue. The only thing you can do is learn the merge.
Look right and left and right and left again, and stare for a good long time to see when the next gap in traffic will be, it's nice when the traffic is staggered so that the car in the lane closest to you is first, then there's a car slightly later in the next lane etc. Because then you can walk out into the street after the first car and continue on lane by lane as the cars pass. Once you have a good feel for the pulse of traffic, pick your time to go and commit. If you start to go, go, and don't stop.
Whatever you do, don't make eye contact with the motorbike drivers. I know this is counter intuitive... in the US you make eye contact so you know that they know that you're there... because they’ll stop for you if they see you. This is just not the case here. If they see an object (you) in the street they will (usually) slow down/ speed up / swerve around you to avoid hitting you... but if you hesitate or make eye contact it throws them off - they don't know what you're going to do. So just start going and keep going. I recommend going fairly briskly, but again, you've got to pace yourself with the traffic. Sometimes going slowly lane by lane stopping in the middle of the street is the only way to get across.
The best thing to do though is to find a Thai person and cross when they do. And make sure they're between you and the oncoming traffic. ;)
If you can do it, go for it. I try, but I never do especially well. The best I can say is that I don't always get as completely ripped off as I might if I didn’t even try. Ask for the price, if possible check a few different stalls before attempting to make a purchase, that way you'll at least have an idea of what the average opening price will be. Offer a lower price, and see where it goes from there. They usually have a big ol' calculator for this purpose. They put in a number, then you put in a number, both of you act like the other person is way off (all with friendly smiles) and eventually you agree on a number. It's a legitimate part of the culture, so jump right in, but don't be a Cheap Charlie either. If you're here on vacation, it's a good bet you make a ton more money than the shop keeper. Haggling over anything less than 50 baht ($1.50) is silly.
So you wanna go to Thailand: #3 Dogs, Farangs & Bathrooms