My department is currently looking to hire new firefighters. This process, for the candidates, is usually long and full of opportunities to fail. Less than 1/3 of 1% of all wannabe career firefighters make it to their dream jobs (the rest become cops....kidding....sort of). I'm going to take you through each step of the process and give some of the pointers that I've picked up. I don't claim to be an expert but I did get the job.
The hiring process starts with the job announcement.
firecareers, that will let you know when departments are hiring. It's much easier to figure out which departments in your area are hiring and their minimum qualifications for applying.
As long as we're on the subject of minimum qualifications, figure out what type of department you want to work for and start getting yourself prepared. If you want to work for a department that does mostly wildland, focus on that. If you're trying to get hired on a department that does not have medics going through medic school is a waste of time. For the most part, departments in my area want you to have an EMT license and a firefighter 1 academy.
Now that you know a department is accepting applications, get one and fill it out. If it's not online than make sure you fill it out legibly. There are a lot of applications for HR to go through and if something is not legible they will usually just toss it out. If they require photocopies of any documents (make a check list so you don't forget to mail something in) be sure the copies are readable. I recommend going to Kinkos (sorry, it's now FedEx Office) and spending the money for a nice color copy. It's an investment. While you're there make more than one copy of each since you will probably need to do this again for the next department you apply to. Once it is all filled out send it in on time.
Next, The Written Exam.