The avodah of Rosh Hashana is nullifying ourselves.

 The source of sin is when we think that we are more important then anything else.  When we think that we are king and we forget to make Hashem King over us.  On Rosh Hashana we have to make ourselves nothing and Hashem everything.

from the Shiur by Rabbi Lazer Brody:

The Ego Barrier
http://lazerbrody.typepad.com/lazer_beams/2010/08/the-ego-barrier.html