Honestly, aside from having the funds and gear ready, and assuming you have no special needs, you don't need to plan much. You'll cross a resupply point every 3-5 days with the rare exception so mail drops aren't necessary. You'll need to plan your gear around your potential start and finish time accordingly of course. Otherwise, wing it and have fun. You can push it and finish fast, or take your time and enjoy the trail life.
Oh yeah, make sure you carry some kind of shelter so you can be self-sufficient. Don't be the guy who shows up at a shelter in the middle of the night and asks if anyone has a tent, and can they please use it because you don't have one.
There are lots of book details you might want, like requirements in the Smokies, etc. but that's standard info.