I haven't yet read through all of the responses, but I might be able to offer some input from the perspective of a prosecutor (albeit a new prosecutor):
1. Take good reports. By good reports, I mean detailed reports. Ensure that you record the statements of your suspects and witnesses. Be detailed and don't leave anything out (particularly statements of the suspect), preferably verbatim. Please, please, please don't try to make the determination of what is or is not relevant for the prosecution to read. Sometimes seemingly innocuous statements prove to be very important and it's always best to have a written record to refresh your recollection before court. Additionally, if your prosecutor's office is like mine and operates with an open file policy, the strength of your report can actually play a huge role in getting the defendant to plead rather than battle it out in court.
2. In that vein, be sure to get your detailed report submitted in a timely fashion. I've had, in the short time I've been prosecuting, more than one occasion where I've had to go to Court without having a report from the officer. That's unacceptable. It jeopardizes that case, and undermines your relationship with your prosecutor's office. You may be the best street cop in the world, but if you can't bring the case home in court, your efforts are for naught.
3. Don't rely on video or audio recordings to take the place of your reports. A/V equipment fails, routinely. Sometimes mics don't pick up everything, the camera isn't at the right angle, equipment breaks, batteries run out, etc. Audio and visual can certainly help you recall what occurred, but it's still better to put things into writing, particularly things that might not be clear in video or audio (i.e., the odor of alcohol, odor of marijuana, bloodshot or watery eyes, etc.).
4. On the point of audio and visual recordings, make sure that they are forwarded to the prosecution in a timely fashion, much like your reports. It's never good for us to be scrambling to get that information from the officer or department on the eve of a court date because it wasn't included in the investigation file for some unknown reason.
5. Get to know your prosecutors, particularly in a small jurisdiction. You're going to work with them, likely for years. Build a rapport with them. Call them (if that is the practice in your area) if you have questions on legal issues relating to what you're seeing on the street, particularly if you're uncertain whether you're about to write someone for the correct charge. Encourage them to ride along with you (again, if that's okay with your agency and their office). I've worked in law enforcement (just a part timer) in areas where the relationship between law enforcement and the defense bar was better than the relationship between law enforcement and the prosecutors. It made for an unpleasant working relationship.