Proper form is the form you feel most comfortable with. Everyone's body structure is diffrent. If you want to add distance then you have to work on rotation of your torso and the allignment of your feet. When people ask me how I throw so far, I show them the very basics of a core throw. Stand parallel to the basket, feet shoulder leanght apart. Point your disc at the basket, then rotate your torso 180 degrees around. Make sure that when you are turned 180 degrees out, that your hand holding the disc is lined up behind you in the same direction of the basket. Then shift about 75% of your weight to your back foot. The one thats furthest from the basket. Now when you go to throw the disc, take your hand and pull the disc towards your chest. Pull it as fast as you want but try to hit your self in the chest. If you do this correctly the natural reaction of you pulling that disc towards your chest will make your torso turn due to the arm speed. Don't worry about follow thru at this time. If you pull that disc towards your chest you will get the follow thru automaticaly.
But just practice that core throw. Once you feel the arm speed, the snap, and see how your body reacts then go ahead and tweek it so it feels good for you. If you need to bend your elbow a bit then do so. Remember its all about what feels good for you.
You can get on youtube.com and watch all the pro videos and how they throw. If you take out all the garbage( by garbage I mean useless motions prior to the throw) you will see that they all have one thing in common.
The best example I can give of this is on the Discraft Disc Golf Clinic: Long Distance Drives. Watch "Critter" Bill Themm and how he throws starting at 2:35 into the video. He doesn't putt any unnessary moves into his throw. I would watch that part over and over and over and try to mimic what he does. Once that starts to feel natural to ya, then add what ever moves you want to your throw.