Form is key. Standing at 5'7", and weighing 135#'s soaking wet, I don't look to be much of a big distance kind of player. But I can consistently hit past 400', and my record is just over 500' during a tournament I played in a few weekends ago. I've only been playing seriously since March of 2009, and I know that I can out throw anyone on campus, save the two local pros that we have at our college.
This said, what I notice about my friends that are often much larger than me, is that there are a few things in our form that allow me to throw better.
1) Pull your arm across your chest. A lot of guys I play with reach down by their waist when trying to get more power on the disc. I find that when they do this, they end up throwing extremely high, or the disc comes off at a 45degree hyzer. When they try fighting this with anheiser, they end up getting a really fast, high rising anny that peters out and dives to the left (RHBH) after maybe 260'. I make sure to pull my arm ACROSS my chest, in a horizontal motion, so that I can get that SNAP at the end. The disc literally ought to pull itself out of your hand.
2) Throw flat. A lot of people when starting to learn big distance seem to be trying to do this entirely on their own. I find that working with the disc you have is essential. This may sound weird, but I often aim at a target just about 4-7feet off the ground half way to the target I'm trying to get it too- that way, I have something to aim for rather than just chucking it. This also gives me the ability to try to get the disc to stay flat, thus allowing it to do most of the work as it utilizes its speed and glide characteristics. I often am throwing things as though there is a tunnel shot with a very low ceiling, and this helps me keep my discs down. You can adjust height of the throw accordingly on if you find yourself burning things off to the right too quickly.
3)Know your gear. One of my friends throws a 162g Dx Valkyrie. He is by no means a weakling- but what I find interesting is that he is backing off so much on this disc, that when he finally does get a great snap, it flies off to the right horribly. When this happens, he ends up telling himself it was a bad shot. Now, while I believe that you could work just about any disc to handle a lot of arm speed, I don't think this is a good choice for him. He will be making so many concessions for this disc that in the end, he won't be able to step it up to something a little faster or more stable, because he'll be used to pampering a super light, beat up disc. You should know what you are throwing- what weight, what the sort of plastic you have and its effects on flight, and the general required speed needed for the disc to achieve its flight pattern.
4) Practice. I learned a lot from going to a field and just tossing. This way, I do three things: build muscle memory for my form as it gets better, learn each disc individually, and get to measure my distance without worrying about whether it was too short (or too far) on a course. You can just let loose. This is helpful if you have someone who knows how to throw far watching you and helping you out. This helped me so much- esp. with my friend and I pushing each other to throw farther than the other.
5) Rest and eat well. You can't just go rip your arm up for hours and hours every day and expect it to get better. You need to take a break and let your muscles rebuild. Make sure you are getting enough protein and carbs to keep up a good workout regiment. I know most people can only get out on the weekends, but throwing every other day for a few weeks, even 20 min., will help your muscles figure it out. Throwing distance isn't going to just magically come to you. You need to work towards it.
6) Have fun. Serious- most of this game is played within the approach and putting shots. Although big opening drives get you that much closer to the pin, I often find my short game is lacking when my long game is to be desired. Just go out and enjoy the sport, and watch for minor improvements all the time- ask for critiques, etc. But just don't let it get to you.
