1. Procrastinating. Putting off a performance evaluation sends a horrible message by signaling that the manager doesn't care about the employee's professional development.
2. Not being direct about problem areas. Of course, nothing in a performance evaluation should be a surprise because the manager should have been giving feedback all year, but bad managers shy away from discussing problem areas, and this often carries over to formal evaluations as well. Sure, addressing problems can be uncomfortable, but you shouldn't be a manager if you're not willing to meet this obligation.
3. Not being specific enough. Managers often write reviews in generalities, both when praising and when offering criticism—for instance, writing, "You're slow in getting your assignments done" rather than, "You turned the quarterly report in late during two of the four reporting periods." It's true of praise, too; you could say, "You did a great job with the new inventory system," but it's more effective to say, "Your revamping of the inventory system has saved the company money, and I've heard several people comment about how much easier you've made it to find the supplies they need."
4. Not paying attention to the overall picture. I've seen managers write lukewarm evaluations for employees I know they love and would be devastated to lose, and I've seen weirdly positive evaluations for employees who need to make major improvements. Managers need to pay attention to the overall message and make sure that the sum of the parts adds up to the correct whole.
5. Focusing only on recent history rather than the entire evaluation period. Managers should resist the temptation to be overly influenced by recent events; the evaluation is (in most cases) for the whole year, not just the past few months.
6. Not getting feedback from others. Managers should be aware that they only see part of the employee's performance, and by seeking feedback in confidence from others who work closely with the person, they may learn things, both good and bad, that are useful to know.
Alison Green is chief of staff for a medium-size nonprofit where she oversees day-to-day management of the staff as well as hiring, firing, and staff development. She is working with the Management Center to coauthor a book on nonprofit management. Her writings have been published in the Washington Post, the New York Times, Maxim, and dozens of other newspapers. She blogs at Ask a Manager.