Read newspapers, magazines, book excerpts, or anything else than contains information: Ask a friend to question you about every little detail. This task will help you improve your memory, an essential tool for prospective police officers.
Write short essays on everything, from the difficulty you had parking your car, to the ending of a movie. This is especially helpful, if you are not accustomed to expressing yourself with words. Ask for professional advice, by academics or writers, on how to write concise and understandable essays. In addition, have them point out any grammar or spelling mistake you may have made.
Break down problems of everyday life and try to find a rational solution. You will be tested on reasoning and judgement: So, think, plan and solve.
Practice your math and map reading. These two skills will be judged during the written exam and are mandatory for successful candidates.
Familiarize yourself with books, movies and TV series revolving around police squads. They can give you a taste of how officers communicate the facts of a crime scene, or a suspect's characteristics. It's entertainment of course, so it's not completely accurate.