I've been working on becoming a firefighter for 4 years now. I've got the CPAT coming up next month for what is supposed to be the best Department in my state.
4 bits of advice:
1- Keep up your conditioning/GPP if you have to do the CPAT.
2- Be patient. All of the firefighters I've talked to had to work for years to get hired. One guy I know is the son of a Battalion Chief and it took him 6 years of applying and getting rejected to finally get hired.
3- Get your EMT-B certification as soon as possible. Some departments won't even look at your application if you aren't certified.
4- Check the websites of the cities you are interested in often. They usually only accept applications for a short period of time once every year or two, then they hire from that pool of applicants.