Here are some quick tips about how to improves your throws;
Practise over a short distance; this is how you learn the technique to be able to throw further.
Keeping the disc low reduces the amount the wind affects it.
Any throw needs two things: spin and forward momentum. If you have the correct grip, you can apply both of these with a simple flick of the wrist.
Don't try too hard. Practising over 10-15m shouldn't require any arm movement.
Release the disc, don't throw it.
Increasing the spin will stabilise the disc. Get more spin by releasing the disc faster, not harder.
To increase distance once you have control of the release of the disc, use your arm and body to add forward force. The angle and spin at release have to be more precise over longer distances. Again, do not throw the disc, accelerate it smoothly in a straight line.
A good throw requires all the forces on the disc to be in line. Prior to release the disc should be at the angle you want it to fly, and move in a line in the direction you want it to go. The spin should also be applied in this sense.
Step out and forward as you throw. One, it acts as a pivot and moves you away from your marker, but two it will put more momentum (and therefore more distance) on your throws.
When looking to huck, you want to get your entire body into the movement, yet still retain good release angle and spin. As you wind up for the throw, store energy in your hips, core and shoulder muscles. As you throw try and unravel from your hips, through to your core, then out to your shoulders and into your arms. It will generate a lot of momentum and help you throw further. However if you can't generate enough spin, all this is wasted. You do this by snapping your wrist as you throw, and it is the single most important part of your throwing action.
Many more hints and tips can be found on the Ultimate Handbook