The key to throwing a good forehand is having good wrist snap. This video shows how you should be snapping your wrist and how with good snap, the disc will have good spin and will have a smooth flight.
This video discusses how to diagnose your throw if it’s wobbling on the release. This is usually due to your wrist ‘breaking’ on the snap instead of keeping your palm facing up. To correct this you can have the disc dropped below horizontal to start and then as you snap, your natural tendency to bring the disc up will have the disc release flat.