Real BBQ isn't anything with out the flavor passed on to the finished product by the sweet smoke from the wood that is being burned as a heat source.
Let's examine what can be used. There is a general rule of thumb with wood selection that any tree that produces nuts or fruit is acceptable and safe for smoking with. Just look at some of the most popular woods used and you will see that this is the case. Hickory, oak, apple, and cherry are among the top picks.
Among those woods that can't be used would be any pines, spruce, fir, cedar or elm. When in doubt, don't use it unless you can verify it's safety.
Here is a rundown of some of the preferred woods to use. This is just a partial list.
Personally, hickory is my favorite. It is a one of the stronger flavors and goes great with beef. Being of a stronger flavor, it is easy to over do it with hickory.
Oak is very good as well and has a medium amount of flavor. It pretty much goes good with everything.
Apple and cherry and other fruit woods have a lighter, more mellow flavor that really shines on things such as fish and chicken.
Pecan. I really like cooking with pecan. It lends a sweet nutty flavor and goes well with pretty much anything. Unfortunately, living in Northern Illinois, I rarely get any. I was down south about 2 years ago and brought home about a third of a truck load, but alas, it is all gone now.
Mulberry is fairly new to the scene as a flavor wood. I'm not sure why, when it is everywhere and people are glad to get rid of them. Talk about a mild sweet flavor, throw a hunk on a fire and you will swear you just walked past a cotton candy stand.
Mesquite is probably the strongest regularly used smoking wood and the most popular in Texas. It is very strong and has a distinctive taste. I will use it sparingly on occasion as it can be easily over done.
There are some others that are different. I have heard grape vines are good to use, but have no experience with them myself. Some people will also use the wood from wine or whiskey barrels. While the smell may be a bit different when burning, I have never noticed a distinct difference in using these over just regular oak like the barrels are made from. Someone else may be able to tell a difference.
Mixing wood will give great results. I especially like to mix hickory and cherry. Oak lends itself well to mixing with fruit woods.
Those are the basics of what types of woods to use or to not use. I'll go a little more in detail soon as far as methods and techniques of cooking with wood.
Thanks for reading!