I spoke on this subject recently for the West Michigan PRSA chapter--my presentation is available on Slide Share if you missed it. That presentation reviewed the basics of being a part-time adjunct or making the transition to full-time professor as either a visiting/affiliate professor or as a tenure-track professor.
But I need to expand on that overview with three general comments related to letters, emails, and applications I've seen recently from some would-be professors:
1. Consider how you tout your experience.
Many professionals trying to impress university search committees include a phrase in their cover letters that they have "actual business experience." My first reaction: of course. We would not expect you to apply for a job teaching PR if you had no experience in the field. That is not a statement that sets you apart--that's a basic expectation for all candidates. I would add, by the way, that PR experience could also be in the nonprofit and government sectors, where a significant number of PR practitioners work. Knowledge/experience of PR in multiple contexts is vital. Secondly, it implies that the full-time faculty currently on staff do not have experience. This is not necessarily true; where I teach and at universities across the country I know legions of professors who teach PR and have worked in the field before. And if they have not, having a PhD and no PR job on the resume does not mean one is removed from reality. Many life-long academics are well informed on PR from their empirically sound research and other connections with the profession. Third, while there's no doubt that work experience in PR is an asset in the classroom, it can also be a crutch. Many new professors rely too heavily on the specific stories from their careers and fail to set them in context, integrate them with larger sets of experience and theoretical implications. That's called teaching, and that's what the job is.
2. Know the job.
When I made the transition from practice to professor, I endured a lot of jokes about smoking a pipe and wearing a blazer with elbow patches. These people were kidding, but stereotypes endure about professors--namely that all you do is teach a few hours a week and then relax. First, teaching is a lot of work--preparing lesson plans, locating up-to-date and useful readings, designing projects and activities, grading, advising, etc. If you are a full-time professor, you also need to consider research and publication/presentation expectations as well as service obligation to campus committees and community activities. I frequently put in more hours per week during the school year than I did in my jobs when I was a PR practitioner.
3. Don't try to change everything--right away
Adjuncts and new full-time professors bring a refreshing new perspective and eagerness to university departments. But be careful not to expect to come in singing "here I am to save the day." Adjuncts and new professors often recommend new courses or even complete curricular overhauls without considering the rationale for the current program, past efforts at change, the national landscape, and the process on campus for proposing new courses. There's a good chance that those on staff already have considered new ideas and decided against them for practical and/or pedagogical reasons. Try to respect that, learn, and then propose innovations once you grasp the historical and curricular context.
So, the best advice would be to stress how your experience is relevant and unique to the university where you are applying, how you understand the program and curriculum and see your place within it, and why you are confident that you will be able to teach well.