Break down the letter into short, but specific, paragraphs. Don’t ramble, but do flesh out your key points. Try to keep it at one page, covering the various aspects of their recommendation in brief, specific detail.
The most effective letters of recommendation are written by professors or work supervisors who know you well enough to describe your academic, personal, or professional achievements and potential with candor, detail, and objectivity. Letters that compare you to your academic peers are often the most useful. Most schools do not consider general, unreservedly praiseworthy letters helpful.