Prepare by getting in the law enforcement environment. The more you know about it the better chances you will have when it comes to a full time sworn position. And I am not talking about watching the TV show COPS, I am talking about the behind the scenes law enforcement duties. For example, I held the following positions to gain as much experience, education, and knowledge that I could:
Field Supervisor of Security for University PD
Community Service Officer for small PD
Reserve Police Officer for large PD
Park Patrol Agent for Park PD
Those positions gave me a ton of experience and contacts to get that full-time sworn position. You learn how to handle people, situations, giving citations, driving squads, learn your strengths and weaknesses, what you want in a department, etc. The minor stuff consists of knowing the department, city, type of law enforcement activity, etc. Anyone can learn that, but the experience that you gain actually working is invaluable.
K9
"The difference between the mile and the marathon is the difference between burning your fingers with a match and being slowly roasted over hot coals."
-Hal Higdon-
"You have to forget your last marathon before you try another. Your mind can't know what's coming." -Frank Shorter-