(1) Give Sincere Recommendations for People You Can Truly Vouch For
This is critical. Your recommendation is not only a reflection of the person being recommended, but of yourself. If your recommendations are not legitimate, your own credibility is diminished. It's best to politely decline writing a recommendation if you are not able to sincerely provide a recommendation of the person's excellence. Similarly, generic, nondescript recommendations are useless and reflect badly on you, the giver. To avoid being perceived this way, always limit recommendations to those you can legitimately vouch for.
(2) Note The Nature of Your Relationship
Before sharing accolades, be sure to frame the context of your recommendation by explaining your relationship to the person. Are you a client? Vendor? Friend? Colleague? Have you worked with this person in multiple capacities? (For example, "I have worked with Kathy for a number of years, both as a client and as a vendor.") Have you used a variety of the person's services or product lines? Explaining the scope of your relationship and experiences with the person increases the credibility of your recommendation.
(3) Avoid Generalities: Speak to Specific Skills, Expertise, and Abilities
Likeability is great, but it's not a differentiator in a competitive market. Nor is professionalism - it's expected. Instead of mentioning these, spotlight what is exceptional about the person. What is the strongest advantage, greatest skill, or most unique characteristic about this person that would be important to a prospective client or employer? Be very specific, and use strong and positive language in your description. ("Dan's background in marketing, coupled with his sense of humor and experience developing online communities, makes him a powerful communicator; he immediately engages prospects.") What results did you reap from working with this person? How has he/she impacted your organization, project, etc.?
As an added bonus to the person being reviewed, consider the keywords that are most relevant to the services they offer. Review his/her profile - what skills and qualities does it list? If you can legitimately confirm these skills, and include some of them in your recommendation, you will reinforce what the person wanted to emphasize.
(4) Keep It Brief
Recommendations should be a quick hit, not an exhaustive review. Don't expound on a laundry list of points - stick to one or two key skills/qualities to tout.
(5) Include a Call to Action
As a final reinforcement, include a call to action that notes the benefit of working with the recommended person. For example, "If you want consistent, reliable property management services you can depend on, hire Kurt."
The best recommendations keep it real. Always make comments that you would make if someone asked you for a reference in person. Avoid sugary fluff, which is always obvious and tends to discredit your objectivity.
What additional tips would you add?