There are tutorials on www.usajobs.com still here are a few more tips.
*When describing your experience, use the KSA format: K- knowledge (what certifications/how much experience you earned for that position) S- skills (what machines you are experienced using? Mention copiers, forklift, printing press, grill, etc.) A- accomplishments (How did you make a difference? What difference did it make? Did you change the way the office/company does things? Did your team achieve its goals?)