There are many reasons an adult dog may not be house broken. It could vary from a medical condition (a virus or a parasite), to never being taught, to even just a behavioral issue. If your dog is suffering from a medical condition, treatment should solve all house training problems. Most house training issues are behavioral issues and are easily remedied.
The very first step in house training an adult dog is to begin crate training him immediately. Crate training your dog will teach him the boundaries and rules of your home. It is also the most effective aid for house breaking and it provides your dog a safe place to comfortably relax. On top of all of these great things, crate training also gives you a reliable location to leave your dog while you are not home.
The second step in how breaking an adult dog is never leave food and water accessible to your dog all day long. By implementing a feeding schedule, your dog will be eating twice a day, once in the morning once in the evening. Like you, when your dog eats at regular times, he will have to go to the bathroom at regular times.
So now it is time to go outside. To make your life much easier, choose a specific location in your yard you would like your dog to use as his own personal bathroom. This actually gives your dog some more consistency and if you bring him to that specific area every time he has to get to the bathroom, he will quickly become comfortable and much more willing to relieve himself there.
The key to any training is in the praise. All dogs want to please their masters. When your dog behaves in a way that makes you happy, let him know by giving him generous praise (lots of scratches and "good boy!"). When he knows what exactly makes you happy, your dog is much more willing to do what makes you happy.
When you are breaking your dog, you must expect accidents. This is a trial and error process for your dog, so when there is an accident, do not get mad. Make a loud noise to make your dog stop relieving himself. Once he has stopped, calmly and quickly bring him outside to where he is allowed to go potty. When he finishes reliving himself outside, praise him. Be sure to thoroughly clean where the accident was, you do not want you house smelling like doggy poo!