In General - My primary advice is to eat local food wherever possible. Most people wouldn’t come all this way to eat at Burger King. Food in Thailand is extremely varied with hot spicy curries prepared with local ingredients particularly popular. Of course for independent travelers there is less exposure to Western class dining and top class restaurants. In less popular tourist areas, those who are happy to experiment will do best. One obvious point I make is not to be afraid to eat in local restaurants and mobile kitchens (roht khen). Often there is no choice with this but one is rarely disappointed with the food. This is a good starting point but there can be an issue with hygiene. My tip here is always select food that is cooked at the time you order wherever you are. There is a strong tendency for venders to cook food in advance which will be left exposed for long periods. This increases the risk of contamination and in any case reduces the quality and taste of your meal. Many roht khen vendors cook food while you wait which is absolutely fine. To give you more idea of where to eat I include a section below.

Mobile kitchens (roht khen) - These appear at all times and in all locations where there is a good footfall. Naturally that includes tourist areas but they are frequently found near offices, hospitals, schools, etc. where there is a local need. Many Thais collect food in this way. Some don’t even have kitchens.
Convenience Stores – Thailand has a vast network of 7Eleven stores but there are many others. They provide snacks and there is the facility to warm food in a microwave or grill. Found often on every street corner they also can be found in filling stations. Snacks are cheap and bridge the gap between local food and more Western types; burgers for example.
Food Courts – These are usually defined by their communal seating arrangement. The traditional types still flourish in towns and cities often in town squares. The night bazaars and markets are also good locations. The food here is very cheap and normally serviced by roht khen vendors. Food courts in shopping malls are also popular.
Shopping Malls – Most bigger towns now have shopping malls with Big ‘C’ and Tesco Lotus superstores most evident. All malls offer international dining. Major international chains can be found here so these are the places to go for those who don’t wish to venture far out of their comfort zone.
Local Restaurants – These are of two basic types. The more general type offers basic food types that are cheap and cater for those on the go. They open early and have meals ready for those on their way to work. Depending on demand they will serve meals through the day but usually close before dark and often close much earlier if they use up their fresh produce. Little is kept for use the following day as Thais prefer to eat freshly prepared food.
The other type of restaurant serves a much different type of customer who, after a long day at work, wishes to go out in the evening and chill out with a few beers. It is here that the amazing range of Thai cuisine can be enjoyed. Again the selection is far too wide to list but to mention just a couple gives one some idea of what to expect. The first group to mention is the seafood restaurants which are abundant in Southern Thailand but just because the ocean is never far away doesn’t mean that seafood is cheap. You may get a cheap plate of crab fried rice in the daytime but fresh crab, shellfish, lobster and sea bass for example can be ten times more expensive at specialty restaurants in the evening at beach restaurants. Inland prices are lower. However the good news is that you would probably never order such amazing food back home unless you won the lottery but in Thailand just treat yourself for once.
Another type of specialty restaurant very popular in Southeast Asia is the buffet grill. There are two basic types; the BBQ grill (Moo Ghata) also known as Moo Yang Gowlee (Korean BBQ) or the hot pot (Jim Jum) also known as Suki (Japanese style). In each case you will be provided with or you can select from the buffet, fresh produce that you cook yourself. Both versions require a charcoal burner. The grill does as it says; you cook meats or seafood on top of the burner. The cooking vessel used is a hybrid of the grill and hot pot so you can grill and boil at the same time. While the grill is multipurpose, the stand alone hot pot is also popular, normally coming in the form of a clay pot. Both these types are relatively inexpensive and are great value for money particularly for families.