Prepare to spend a couple of hours on the door adjustment. First, with the door almost closed, try lifting the back of the door up and down. If you can, your hinges are worn, and will need bushings and pins. If there is no measurable amount of movement, proceed to the next step. Using masking tape, mark the exact location of the striker. Remove the striker, and close the door. Check for body lines lining up, gap equal all around, etc. If anything is out, you will have to remove the kick panel to get at the fasteners on the inside, and adjust. On the door side of the hinge, you can adjust for in and out, as facing the door. On the pillar side, you can adjust for and aft. Once you have everything lined up, reinstall the striker plate in the original place, and just snug the fasteners. Try closing the door. As you close the door, you will see the top of the door try to move up or down. Tap the striker lightly with a hammer, so when the door tries to close, it still lines up with the body line. Once you have the up and down right, then start on the side to side, until the door is closed and the body lines are even. Once you have everything aligned properly, tighten the striker screws.
Its fiddly work, but with a little patience, you shouldn't have a problem. Hope this helps, Bob