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.
Make comparisons to illustrate their success. To put the candidate’s accomplishments into perspective, include comparisons so that the recipient will have some basis to understand why you are recommending this person.