Too little rotation, by placing the right foot down too early can lead to the thrower moving to their right, while over rotation (late right foot plant) can lead to the thrower moving to their left. A late foot plant also leads to a late "catch" of the hammer. This does one of 2 things: decrease the time in double support phase where you apply force to the hammer or you take the same amount of time and release late. Use an active left leg to get the right foot around and achieve a full rotation.
2) Release too high or too low
If your release is too low, your orbit may be too flat and you should increase the angle of orbit. Also you may not be following thru on your throw and "throwing thru the point", ie. throwing thru your proper release angle. Releasing to high is rare in hammer because to have such a high orbit will usually pull you off balance and probably to the ground. The hammer can also hit the ground.
3) Improper Countering
By improper countering I mean not sitting your butt down and keeping the weight on your heels or leaning forward with your upperbody. These lead to a loss of balance and a poor throw. Try sitting back flat against a wall and squat down to the correct position (~90 deg.) Remember to keep your arms out. Also do this with a partner, countering each other.
4) Not having any weight on the right leg on release
If your weight is on your left foot, chances are you will be pulled out the front-right of the circle upon release. If your right foot isn't solid in contact with the circle there is nothing to absorb the back force of release ie. no block. (Newton's Law: For every action ther is an equal and opposite reaction). Focus on a straight right leg in your phantom throw and do a few wind and releases to get the feeling for it.
BEGINNER
Foot drills - back and forth across the circle
Winds - 3*10
Turn drills - to get the footwork down before turning with a hammer
Wind and release - 10
Choppy step throws - 5-10
1 turn throws - 10
Wind and turn drill - 5
NOTE: Make sure the footwork is mastered before turning with the hammer. Once a 1 turn throw is mastered, jump to 3 turns. And in practice turn as many times as possibe AFTER a 1-turn throw is mastered (even sets of 10 turns in a row)!!!
ADVANCED (3 turn thrower)
Foot Drills before they start and turn drills between throws.
1 arm winds - 2*10 each arm
Multi-turn throws (for rhythm) - 3-5sets of 5-10 turns
3 turn throw - 3-6 at multi-turn speed
5-10 with the 3rd turm sped up
3 MAX DISTANCE THROWS
5-10 more throws at 80% of max speed