Nothing will drive a human resources person over the edge faster than an applicant who can't produce the necessary paperwork. Before you even start the application process, put together a file of the necessary certifications, licenses, and so forth. Have fresh, clean copies ready for presentation. Hint in dealing with civil service or human relations: Make their job as easy as possible; have your packets ready and complete.
Read the job description.
Fully understand the entire job description. Some cities have residency requirements with exceptions for the military. Some require everyone to live within their jurisdiction within, say, a year of hire. Can you afford to live in the city or county to which you're applying?
Some have other requirements. I mentioned tobacco use being an issue. Other agencies will eliminate candidates who have visible tattoos or piercings, recent (or sometimes any) drug use, and criminal convictions or traffic violations.
Think, what is on your record that would remove you from the list? Read the fine print and if you don't understand, ask to have it clarified.