Classic
For lack of a better term, this is probably the most popular type of restaurant. You can get the usual panoply of dishes, some seafood dishes, and some noodles.
BBQ
These are the ones where you see the ducks and chickens hanging by the front door. They are the equivalent of Cantonese fast food, although it's far better quality than what you would find in your average burger joint. They're not as classy as the classic or seafood restaurants, though. Roast duck, chicken, and pork are their strong points. You may also see the walls plastered with vertical pieces of paper filled with large Chinese characters and a price underneath. They are menu items. If you can't read them, don't worry about it. If you're really adventurous, point to a few at random and ask for them. Ignore all of the wait staff's attempts to dissuade you. They will respect you immensely as a true foodie. Or they might consider you a nutcase.
Dim Sum
They serve dim sum, which usually consists of small trays of dumplings and other goodies that you can order from carts pushed by waitresses. A new, emerging trend is ordering these dumplings from a menu, and the staff brings it to your table. The main advantage to the carts is that you can look at the food before eating it. But it can get overwhelming if you're not familiar with the foods. Unlike other types of cooking, you really can't ask them to customize these for you because they prepare them by the bushel in the kitchen. If you want to get the best, go to these restaurants by the late morning before they run out of the good stuff. Dim sum is almost always limited to morning and noon times. Almost all restaurants serving dim sum are classic or seafood type of restaurants. During dim sum hours, you can usually order some other dishes (e.g. chow mein), but it might take some time because the kitchen staff is still preparing the dim sum.
Seafood
Isn't it obvious? They primarly serve seafood. You also find the dishes from Classic-style restaurants. Usually, these places will have huge tanks of live fish, lobsters, crabs, and shrimp. You can order regular fish (i.e. no longer liviing) from the menu at the stated price. If you order the live ones, you'll be charged per pound. The food is fresher, and they'll probably bring it to your table for inspections. Look at it closely (but not so close that you get sprayed by a flapping fish). Pretend you know what you're doing, give a slight, non-chalant nod to the waiter, and resume conversing with your friends. They'll be really impressed even though you couldn't tell a good fish from a bad fish unless it came with a USDA label.
2) Never order spicy Hunan or Szechuan-style foods in a Cantonese restaurant. Many Cantonese think that a bell pepper is spicy, so they aren't all that great when it comes to making spicy foods.
3) If you're in a nicer restaurant, especially the seafood ones, ask if there are any daily specials. Sometimes, these are listed in Chinese. Sometimes, they aren't listed at all.
4) If you don't speak Chinese, look around and point to dishes that you like. The staff will invariably take pity on you and try to help you out.
5) If you order fish, a half/whole duck or chicken, you can expect to find it delivered to your table with its head still attached. Do not panic. It can no longer bite you. If it really bothers you, ask them to remove it before they bring it out. If they forget, stick it on a chopstick and use it to gross out your friends (assuming they don't eat it, of course).
6) Order your dishes with less oil Frequently, cooks will add some extra oil to make the dish look nicer. But it is otherwise absolutely unnecessary.
7) Order your dishes without MSG. If the staff doesn't understand, say very slowly, "mo-no-so-di-um-glu-ta-mate." After they give you a strange look, say "No May Jing" (pronounce "May" as in the month and "Jing" as in singing "Jingle Bells"). All jokes aside, just about every waiter/waitress knows what MSG is.