It depends on what the issue is, but in many cases you can tweak or shim the hinge side. To tweak it - open the door, place a 16P finish nail between the two leaves on the hinge you need bumped & slowly close the door - not all the way but just enough to open the hinge.
Looking at the second picture you might want to install a larger screw in the top hinge to help pull the door back in place - this also brings us to another trick which is closing a hinge back up (this is tougher on exterior doors) but essentially with the door closed you would use vice grips on the top & bottom part of the exposed hinge (not the barrel) & squeezing it together
Sweet, it worked to correct the sagging!! Unfortunately the light still leaks through at the bottom of the door, it appears the frame or door is warped/twisted slightly. The bottom of the door sits towards the inside of the house, the top leans towards the outside. On the hinge side the door is even.
Here are some photo's showing what I'm referring to, hope they make sense:
Unbelievable... Sean shared an old-timer carpenter trick online. Dude, that's 20 demerits for you. In order to become qualified to learn those tricks, a newbie has to spend 6 months on the job fetching coffee, dense-packing the dumpster with gnarly debris, and humping 2x12-20' rafters up a shaky ladder to the roof.
Seriously, Bob, I wonder if part of the problem is that the door is no longer parallel to the jamb. When I see light coming through along the latch side near the bottom, I figure the door might be warped. Fixing that is a trick, and sometimes it's not possible without major surgery. Also, is there a piece of weatherstripping missing on the head jamb?
Personally, I'm undecided about the ROI on minor weatherstripping tune-ups. You have to hang a new door to correct some of them, or pull the jamb and re-hang it. It can be a big deal. If there are lower hanging air leaks in the house, I'd hit those.
The head jamb has magnetic weatherstripping, it makes good contact so I left it alone. I think you're right on about the door not being parallel to the jamb, and it's a steel door so I'm afraid the door frame itself is what's not right. If the door wasn't North facing I wouldn't worry about it, but when we get those 20+ MPH North winds in winter you can feel the air coming through the crack. If it involves removing the door frame or other major surgery I may just leave it alone. I've even thought of upgrading the storm door, but we're back to the ROI thing.
Bob, if you open the door about 6" and lift on the door, up and down several times, do you feel any play. Tight hinges will provide no slack. Worn hinges will allow the door to fall away from the hinge side at the top and in at the bottom and you will feel some slop when lifting as above.
Bob, with a steel door, you might just try brute force. Put a block of some kind in between the door and the head jamb, something a couple of inches thick. Then, close the door against it and apply some force at the bottom. You need to do this very carefully, a little bit at a time, but you may be able to bend the door enough to make contact the full length of the latch stile. With a wood door this will never work, but you might get lucky with that one. You have to be sure you are not doing any damage to the hinges or the jamb itself.
Of course the other thing to do is to take off the trim on the latch side, cut the nails behind the jamb with a sawzall, move the jamb in a bit at the bottom, renail it, then re-foam the gap and reset the trim.
A quick and cheap fix to a twisted frame (or door) would be a door stop-type weatherstripping that could be attached to the latch side of the frame with the door closed, so as to snugly fit against the door as it presently latches. It might look less obvious if you did both legs and the head as well just for uniformity.