John Shaw, an HR Recruiter for the federal General Services Administration, points out in The Federal Career Guide, the 3 most common mistakes that recent grads and students make in their applications or during interviews:
1. Incorrect spelling and poor grammar in their applications.
2. Not becoming informed about the employer prior to the interview. This is inexcusable with all the information available on the web.
3. Not following up with the [employer] after the interview.
These 3 items are basic to all applications and interviews, not just with the government.
Follow-up can sometimes be difficult with on-line applications, but is necessary in order to determine if your application was received and is complete, at the very least. A polite and professional phone call can give you the information you need, and may even be the opening you need to request an interview, so make the most of it.