My first admin assistant told me what he did -- he moved to MD (2001) and then applied for over 100 Federal jobs. I was the first one to interview him (I was new myself, and didn't realize I was "supposed" to move slowly), and so he came to work for me as a GS-7. Now he's a GS-11 in a bigger and better job.
It is absolutely imperative that your resume be typo free -- this is what the hirer sees.
Work the buzzwords for the position announcement into your resume or essays -- this helps get past the first filter in HR.
Don't apply for any jobs whose open-to-close interval is a week or less -- these are taped for somebody internal. Two weeks may or may not be a reasonable open period.