There are two extremely important concepts I have finally gotten my head around about disc golf. One is understanding the power zone and the second is to throwing the disc around the pivot point. While I could sit here and explain these concepts in the detail, it would be much easier for me to direct you to the resources I used to better understand the concepts.
These videos are from a gentleman named Bradly Walker over at the discgolfreview.com forums. He does a good job explaining how to get the most snap out of your throw.
The power zone or the hit, is when the disc is near the right pec (left pec for lefties), elbow punching directly towards the target, hips rotating through the throw. For the most part, it really does not matter what you do up to this point, as long as the disc is close to your chest and you hit every point mentioned above, you will throw the disc far. Here is a video from Dan Beto from the discgolfreview.com site. He is known to just be a monster thrower. In this video he will teach a drill to work on the "hit", which is the power zone I mention above.
While I do understand these concepts its something I have to work on everyday until muscle memory takes over. Bruce Lee onces said it takes 10k reps of a movement to full absorb. This is why field practice is so important. You get WAY more reps focusing on exactly what you want to work on.
Practice and work on the above concepts and you will be throwing 400ft+ soon enough!
Good luck on the course!