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.
Do graduate schools care if letters are confidential or not? In general, graduate programs prefer confidential letters. Admissions officials say that it displays more confidence on the part of the applicant if letters are "confidential" (meaning you, the applicant cannot see the letter). The Letter Service is required to indicate on the letter if it is confidential or non-confidential.