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.
Keep your writing action-oriented. Begin each paragraph with a punchy, active affirmation of the candidate’s qualities or character. Strong verbs are your friend.