For development jobs I've never have to do staff applications because my work speaks for it's self. Saying this I've only done 1 staff application in the past year and it was for FAQ on Graal Kingdoms but mind blanks were not really a problem because I knew what I wanted to say and why I wanted the job.

Don't ever think your application is wrong when you know you'r able to handle the job you'r applying for.
Tell the truth, show your skills, and you'r all done ^^