There are a number of cuts labeled pork chops. Bone in or boneless, loin or rib chops, the most important factor to consider when grilling pork chops is the thickness. Thin cut chops (under 3/4-inch thickness) need to be handled differently from thick cut pork chops (anything over 3/4-inch thickness). Thin chops will dry out faster so they need to be cooked quicker, while thicker chops need time to get cooked through the middle without drying out the surface so they need to be cooked slower. It sounds backwards, but it works. Before we get grilling pork chops though we need to maximize moisture, tenderness, and flavor.
Brining: Brining is a great way to add moisture to any meat and is particularly beneficial with pork (see Brining Pork. The real benefit however is going to be with thicker cuts of meat. If you are using thin chops brining may not be the best way to go but if you are using thick chops then a good brine will certainly help. A brine is a salt water mixture (about 1 tablespoon table salt to a cup of water) that gets soaked up by meat. Brining thick cut pork chops should take 2 to 4 hours. Remember to thoroughly rinse the chops after brining to remove any excess salt.
Marinade: For thinner chops a good marinade is the way to go. Marinades can not sink into meat like a brine will but it adds a protective layer to the chops while letting you add loads of flavor. A good example of a basic marinade is Italian Dressing. It contains oil, vinegar and water as well as herbs and spices. Thin chops can be sufficiently marinated in as little as 30 minutes. The marinade will tenderize the meat and protect it from the intense heat of the grill.
Dry Rub: You can always skip the brines and marinades and simply season the surface of your pork chops with herbs and spice (or salt and pepper). This will not add moisture or help to tenderize the chops but it will add a lot of flavor. I only recommend this method if you are going to grill your chops below medium. Over cooking will leave you with a chop that is too dry and tough.
Combining: Brines contain salt so nothing else you do to the chop should have salt in it. You can brine and dry rub, just choose a rub without salt. I do not recommend brining and marinating since they will work at cross purposes. Similarly if you are marinating, then you are already adding the rub, you are just putting it on with the marinade.
Grilling Thin Pork Chops: Thin chops should be grilled hot and fast. This is really one you shouldn't step away from since thinner pork chops will cook so fast. The trick is to grill them like you would a steak, over an intense heat, flipping as little as possible. Preheat your grill to as hot a temperature as it will go. Place the chops on the grill and close the lid for 1 minute. Open the lid and rotate the chops 45 degrees without flipping. Close the lid for another minute. Now flip the chops over and close the lid again. After a minute rotate the chops 45 degrees and finish them off. With a hot, hot grill and thin chops you should have them off the grill in 4 to 5 minutes.
Grilling Thick Pork Chops: Thick chops need a slower heat to get them cooked without drying them out. What you do want to do however is sear the surface to get them cooking. Preheat your grill as high as it will go (if you are using charcoal build your fire hotter on one side for searing with a cooler side to finish them off on). Put the chops on the grill and close the lid. After one minute open the grill and flip the chops. Close the lid for one minute. Now turn down the heat on your grill to medium (or move the chops to the cooler side of your charcoal grill). Rotate the chops to get your cross hatch marks and let them cook for about 3 more minutes with the lid down. After this time flip the chops over and continue cooking for about 4 more minutes. It is best at this point to turn your grill down to its lowest setting (or close the vents on your charcoal grill). Allow pork chops to continue cooking until the center reaches 145 degrees F.
Resting: Once the chops are cooked the way you like them get them off the grill. Place on a plate and cover with aluminum foil for 5 to 10 minutes to let them rest. This recovery period lets the meat loosen up and the juices flow through the pork chop. This really is the most important part of the whole process.