Hey Jeremy,
Becoming a diver is fast and easy. Becoming a Public Safety Diver is another story all together. Once you have your open water certification, (can be had in a matter of weeks), you can dive. At that time I would suggest getting in the water as much as you can. The basic SCUBA skills you will be developing are important to recreational and P.S. divers alike. Once you get some bottom time under your belt, I suggest an advanced open water course as well as a rescue. All the while you will be getting familiar with the system and the way your team trains and dives.
This beginning time of your entry into the team is very important. You will be learning all of the aspects of the dive scene. The job of the tender is the most important one at the water and to master that is going a long way to being a P.S. diver. You will be entirely familiar with the gear, line signals, protocol and operations.
Normally, your team brass will determine when you are ready to take the P.S. diver course that is given by the agency whose system your team uses. After you complete that course you will be an apprentice diver, and will be expected to perfect your skills while operational until you display on a regular basis the ability to get the job done safely.
I couldn't have said it better myself. I recommend getting some information from Lifeguard Systems there web site is www.teamlgs.com. From what I have learned Lifeguard Systems teaches the safest stuff out there. Please keep in mind this is only my opinion and others may feel differently. They offer a Rapid Deployment Class that would be a good start after all the open water stuff is done and you have been given the green light from the department brass. I have 12+ years on the Dive Team in my dept. So if you have questions you can contact me.