Being Objective: Take the emotion away.
Your employee rubbed you the wrong way, you have a disliking towards someone, you hold a grudge because they disagree with you - all these need to be objectively analyzed, the emotion squeezed out, so only the 'lessons learned' stay. For example, let's say in a meeting your employee, in front of your peers, contradicts you and you did not like that. Look at that situation objectively - did you bring that employee up to speed with your perspective prior to the meeting? Did you provide reasonable explanation or attempt to table to conversation within the meeting? Did you have an offline conversation with that employee in the past to allow them to voice their disagreement in private rather than in an open forum? If there is a behavioral pattern, has that been discussed prior to doing their review? Is the employee even aware that you have an issue or concern regarding the behavior/demeanor/approach?
Take the emotion out and have an objective conversation with them based on observations, not inference. Outline what the issue is, and propose a gameplan to help improve on the issue.
Being Organized: Arrange your thoughts & feedback in bullet points.
As a manager, delivering reviews can be stressful, but think of the person sitting across from you who is anxious and nervous about what could be in their review. Writing a review is hard - and it should be. It should involve you, as a manager, thinking through and giving credit where credit is due, and providing structured feedback where the person can focus on over the foreseeable future. If all this gets hidden in paragraphs of text where the content is not broken out by topics, you can almost guarantee that as soon as the person walks out of the meeting, so does the information provided on the review. Bullet point everything - it will help you keep your points succinct, and allow your team member to focus on each point and discuss those one at a time.
Concrete-ness: Provide measurable concrete examples for each bullet point in each area.
Don't be vague like 'he worked on several projects and launched them'. Outline the projects they worked on and what made them successful (or not). For example, 'John worked on the website development project, negotiated and documented requirements, and managed the development and release aspects to deliver the project to meet the marketing campaign slated for the month of June, increasing the revenue by 40%'. Specific data points provides the employees with something to reflect upon, and it memorializes the successes (and failures). If someone's error rate is high, instead of saying 'her error rate reported is too high', say 'her average error rate is 25%, which is 10% above the team average; It is recommended that she attend the following training courses to reduce the error rate...'. Metrics are concrete, irrefutable, and provide direction for the employees.
Constructive: Don't be negative.
It is easy to be negative. It is easy to say how someone is bad at something, but what are you, as a manager, doing to help them? Are you mentoring them? If, for example, a PM is frustrated with the Product Manager and it is impeding the success of the project, you can note that observation in the review, but also outline what can be done to resolve the issue. Perhaps a pointer is to articulate that the accountability of the project's success relies on the PM, and that you will sponsor certain classes where the PM can learn the human side of project management. If there is no plan being offered by you to help your employee, they will see the review as an opportunity for you to tell them that they suck. That's not your goal.
Honest: Do not sugar-coat.
Be open and honest. If you sugar coating issues your message will get lost. Be open to discussing the points you outlined in the review, and if you realize you made a mistake in certain metric, be open to changing the review and don't take offense to it. The review should be a vehicle for a dialogue, not a king telling its subjects what they did.
Be the manager your employees deserve - consultative, collaborative, and provide guidance and mentorship without being overbearing. A performance review is an affirmation of the success, and a recap and formalization of areas of improvement and goals for the next review cycle. A review is the best way to communicate your intentions and expectations, so as a manager, take it seriously.