One of the most important things to remember is that there are no magic bullets. You can't just tell people to do better and expect it to happen. If you want to improve employee performance, you have to put in a lot of hard work. The first step is to understand what's going on with your employees. Is their job easy or hard? Are they stressed out? Do they feel like they're being held back by the company? Knowing this will help you figure out how to get them excited about their work again.
Next, you'll need to come up with some methods for improving performance. Maybe it's a new set of policies for dealing with employees who aren't performing well; maybe it's having weekly meetings where everyone discusses what went wrong in the previous week and what they're doing differently next time around; maybe it's training people on how to solve problems or write reports better; maybe it's giving them more responsibility or hiring more people so that everyone has someone else who can help them if things get too busy at work; whatever it is, make sure that whatever method(s) you choose are ones that are backed up by data and research (so don't just decide "hey this will work!").