Spell out the details of this person's accomplishments. Remember that the committee reviewing recommendations can only base its decision on what you submit. Take your time to be specific. Help the committee understand what this person has done. Imagine that none of them has ever met your nominee before, and go from there.
Be clear, and give specific examples that support each of the awards criteria that you think your nominee represents. It's even better if you can give examples for each one of the awards criteria. The more examples you give, the better sense of the nominee the committee will have.
Remember, you want to show that your nominee is an all-around talented individual, so give examples of that person's accomplishments throughout the last year; don't just focus on one specific accomplishment.
Provide supporting letters. Two (or three) letters are better than one! Ask people who have worked with your nominee in different capacities to write letters of support. Look for students who worked for or with the person, or staff colleagues past or present who might be interested in contributing. The nominee's supervisor is also a good person to ask to write a letter of support.
Use specific and descriptive wording. Don't just say that "John did a good job of planning the department's event," but be detailed! For example, "John's work in planning the department's event involved meeting individually with each office and with students to understand their needs. From here, he collaborated with those same offices to make this year's event an increased success, and better attended (over 300 people came), than ever before."
Don't forget the deadline! It can be a challenge to find the time to put a really good nomination together, all before the nomination process ends. But remember that your hard work will be worth it, so plan ahead!