If you don't have good writing skills, you're not going to get very far in writing for a public relations agency. Spelling errors, typos and poor grammar will make your clients look bad, so don't expect to get very far in the hiring process if you don't know the difference between "there" and "their." That said, though, even the best communicators sometimes need to brush up on their skills -- especially when taking a test that determines whether or not you'll get the job.
Ask the Employer
The first step in the process is simple: ask the hiring manager what you can expect. She may not give you exact details about what will be on the test, but she may give you some hints about how to prepare. Generally, tests of this type include a section that tests your grammar, which might include multiple-choice or fill-in-the-blank responses. You can also bet you'll be asked to write some copy so the employer can see how well you write under pressure.
Research the Company
Get familiar with the PR agency's expectations by reading some of the materials the agency produces for clients. Check out the firm's website, Facebook or Twitter feeds, which may include links to press releases or other recent PR materials. Take note of the agency's style and whether that style changes depending on the client. If the company's website lists its clients, check out the clients' websites. During your test, you may be asked to write a piece of copy that mimics the style of one of the firm's clients, so be prepared to adopt the right tone.
Review educational materials from your school days. Review any textbooks or notes you may need to familiarize yourself with writing or marketing lingo you have forgotten. If you've been out of school for a while, do some research on current trends in PR, marketing and media, so you'll be aware of the hottest new social-media format or why companies are turning toward a certain style of writing.
Since grammar is such an important factor in these tests, it is also a very good idea to review some of the basic rules of grammar. "The Elements of Style" is a classic, a necessary tool for any writer. The Associated Press Stylebook is another good one to review. If you know the PR agency uses another style standard, such as the "Chicago Manual of Style," review that also.