Don’t exaggerate -- show where and how they can improve. Don’t put the candidate on a pedestal. Not only does it not look plausible, it will also set expectations for them that will be next to impossible to meet. If they have an Achille’s heel, don’t exaggerate it, but don’t hide it, either.
Be specific about the candidate’s qualifications and successes. Describe what the person has done using specific instances and examples, rather than generalities. Whenever possible, give evidence or stories to back yourself up.