What's your personality style? Go out and take the Meyers-Briggs assessment if you haven't already. Which traits will help you as a ScrumMaster? Which traits might hinder you?

Talk with others. Get feedback about your performance during meetings with respect to your verbal and written styles, effectiveness of communication. See if you can tease out criticism and areas for improvement. Don't forget to celebrate the things that you do well.

Set up a bi-weekly leadership meeting with fellow ScrumMasters. Identify books to read, blogs to follow, things to try. Report back to each other, critique each other, help each other improve.

When you feel threatened, what makes you feel this way? Is it a person? A communication style? A situation that brings out feelings of inadequacy? Once you've identified the trigger for your feeling, try to pinpoint why you feel this way. Are you afraid of losing? Appearing dumb? What reasons do you have for feeling intimidated in certain situations? Are these reasons legitimate? Even if they are, there must be one thing you can do to start to change the situation. Maybe it's your reaction. Identify and practice it.

Pay attention to what you say for one week. Write down every statement that you make that has a negative twist. Evaluate this at the end of one week; did you have many? Did these tend to fall within the same categories?

Do you have a Scrum buddy? Get one if not?