Many photographers enjoy the experience of working with film and creating their own photographic prints, and professional photographers often have their own private darkrooms so that they can work in comfort. Amateurs are often limited to rented darkrooms or shared darkrooms, which can be frustrating, and it leads some people to wonder about setting up their own darkrooms. In fact, it is relatively easy to set up a home darkroom, as long as you have enough room and you observe some basic safety procedures.
Before you start, you need to think about the fact that many developing chemicals are toxic, and they often smell bad. If you want to set up a darkroom, you should consider how you are going to secure chemicals so that they cannot be accessed by children and pets, and how you are going to dispose of chemicals. Dumping photo chemicals down the sink is not environmentally ethical, and it can seriously damage a septic system.
Once you have considered whether or not you think you can handle the chemicals safely, you can pick out a space to set up a darkroom. Ideally, you should dedicate a room for use as your darkroom, since it will make the darkroom much easier to manage. Obviously, the room should have limited sources of natural light, as this will make light-proofing much easier. You also need running water and electricity in your darkroom, and a fair amount of space, since you need room for developing tubs and enlargers.
After picking out a space to set up a darkroom, start by making it light proof. Use heavy black plastic to block windows, and blackout curtains around the door, so that if someone opens the door while you are working, it will not flood the room with light. Set up a safe light with easily accessible switches, and designate clear wet and dry areas. You want to minimize cross contamination between these areas, as you don't want photo chemicals on undeveloped paper, or electricity right next to your rinse bath.
Ventilation is also extremely important. Many photo supply companies sell light-safe ventilation fans along with other darkroom supplies which you will need, like an enlarger and photo chemicals. Install a ventilation fan before you begin any work in your darkroom, and check to make sure that it works. Long term inhalation of photo chemicals can be very dangerous. Organize the space well, and provide lots of dry, safe storage for extra chemicals, film, and undeveloped paper. Consider setting up a long trough or sink for your developer, stop, fixer, and rise baths, as it will minimize the risk of splashes and make cleanup easier.
Once you have everything laid out, start developing! You may need to make small adjustments after you set up a darkroom and you actually start using it, so try to design the space so that it is configurable. You should also be aware that it is more challenging to set up a darkroom for color developing, since it requires more rigorous light conditions, along with some very nasty chemicals; you may want to leave color developing to the pros.