The brief that turns a generic letter specific

Add a short note — five or six lines — on what you hope the letter can speak to. Not what to say, but which of the things they saw would be most useful: the project you rebuilt after it failed, the seminar where you argued against your own position, the term you were visibly struggling and what you did about it.

Most referees are glad of this, because the alternative is guessing which of thirty students they are being asked about this week. It is also the moment to say plainly if there is something you would rather they left out. And if they cannot write warmly, this is usually when they will tell you — which is a favour, although it will not feel like one.