If its under 40 feet up and not buried deep in branches, a stick or rock works for me. If its higher, or in an unclimbable tree or buried in branches I bring out a tool I made that always works. Take four or five heavy square 3" washers tightly tied together. Attach them securely to 50 to 80' of hd 1/8" flexible cord. Hold the end of the cord not attached to the washers in your left hand (for RH throwers), and with your throwing hand grasp the other end of the cord 3 to 5' from the mass of washers. Swing the cord until it reaches the desired speed and release on a trajectory that takes it OVER the branch the disc is lodged on.
The washers will snag the branch allowing you to shake it vigorously until the disc falls. As an alternative, you can lower the washers through the branches until you can grab the washers and the other end of the cord and really give it a shake. Once the disc is down a few shakes of the cord and the washers descend into your waiting hand.
This tool has NEVER failed me. Well worth the small space it takes up in my bag. YMMV
Note: If you are concerned that the square washers might get stuck in the tree, try round washers. I chose square washer because they catch the branch more easily and I've never lost them up a tee in the five years that I have been using this method.