The basic formula for a brine solution is 1 cup of salt (preferably without iodine) to one gallon of water. This is a very good rule to follow. While under-brining won't have a negative effect of foods, over-brining can be disastrous. Either using too much salt or brining for too long will leave you with a cut of meat that is too salty to eat. Don't worry about the 1 cup of salt that's only 1 tablespoon per cup of water. The solution should be salty to the taste but not thick with salt. This formula assumes that you are using regular table salt. If you are using a coarser salt, like kosher salt you will want to add more, about 1 1/2 cups per gallon. This is because kosher salt weighs less by volume.
When it comes to the amount of time you want to brine something it is more important not to brine too long than not long enough. While some cuts of pork can use days in a brine, even a relatively small amount of time can be helpful. Pork generally takes a long time to get the full effect. Now I wouldn't bother brining a cut of pork if you didn't have at least a few hours but with smaller cuts even 3 or 4 hours can do the trick. Do not; however go longer than the times on this chart.
Pork Chops (about 1 to 1 1/2 inches thick) - 12 to 24 hours
Whole Pork Tenderloin - 12 hours
Whole Pork Loin - 2 days
Brining times are not only determined by the weight and thickness of meat but also by the grain of the meat. Pork tenderloin takes less time to brine by weight than do pork chops because the long running grain pulls the brine into the meat.
The most basic seasoning that you want to add to your brine is a sweetener. This can be sugar, brown or white, molasses, or maple syrup. As a general rule add 1/2 cup of sweetener per gallon of brine. As for how much brine you will need, consider the size of the container you are going to use and the size of the meat you want to brine. A brine solution should be enough to completely submerge the meat you want to brine.
Additional seasonings can be derived from any recipe you might be using or your own preferences. Herbs and spices as well as garlic and onions will add flavor to pork. Try not to overpower the flavor of the pork but just add a hint of flavor. Garlic and onions should be minced or chopped to expose the maximum amount of surface area to the brine solution.