Timeouts are also effective. If your bird bites you hard enough to draw blood, that should be an immediate timeout. And as ChrisWink pointed out, shoulder privileges must be earned. If your little guy is nippy, he shouldn't be up on your shoulder.
Always use a firm and even tone of voice when telling him no. Try not to yell, as they might find that amusing and seek to make you repeat the behavior. Remember, they font automatically understand what you mean when you yell. They learn through association. So work on having him/her associate bad behavior with timeouts.
I can see from your posts that you regret using physical punishment on your bird. I'd suggest that you prevent it from happening again by only working with him/her when you are not in a frustrated state of mind.
Oh, and one other thing. While you want to work on bite pressure training your bird, you should also carefully consider whether anything in the environment might be triggering the behavior. Any changes in the surroundings or even with you. New glasses? Different hair color? A hat? Cologne?
Also consider if it tends to happen whenever someone else walks into the room. If that's the case, it could be displacement biting.
Lastly, you should consider whether your bird has enough going on to keep his/her mind occupied. Training exercises can serve to bleed off some of that excess physical and mental energy so that they don't feel like bouncing off walls when sitting on your shoulder.
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