Hanging a door is a real skill, which is why we would always endorse that you get a professional to do it for you. You may think you can save money or time by doing it yourself, but it can be a false economy to believe this.
1. Contact some professionals. Even if you get a builder or carpenter to hang your door, there is still a lot you can do and a lot you can learn. For instance, if you contacted an expert about hanging a door they would probably want some information before they quoted you and if you can give them that information without them coming to your home you are likely to get it done more inexpensively. For example, you can tell them whether it's inside or outside, large or small, what quality you want, etc. You can know about external hardwood doors via http://www.solidwoodendoors.com/external-doors.html.
2. Informing the professional who you'd like to do the job for you can help them determine precisely what you want fairly quickly. One of the most important things is telling them whether it's an external or internal door you want. The regulations and requirements of these are very different as too are the prices. But this simple piece of information is the most fundamental they'll need to start resolving your requirement.
3. Dimensions and positions - Hanging a door involve knowing the weight and size of it and whereabouts you want it fitted. Passing this information to an expert can also help.