Another note on grip - when practicing gripping tightly you'll often have a weird throw commonly called a "grip lock." A late release where the disc goes buzzing off with WAY more speed than you usually feel like you can throw a disc.
When you have a grip lock REMEMBER the sensation out of your hand. You want the sensation, but you want to bring it to accuracy. If you accidentally grip lock a throw the proper way to use it to learn is to remember the sensation, because that's the sensation you get when you have more velocity on your throw. The late release gives the arm more time to pick up speed. You want to find that same arm speed with accuracy.