How do you write your own recommendation letter?

My former boss asked me to write my own recommendation letter. I’ve seen a few but I don’t really know what’s supposed to be in them.

I was an articling student (i.e.:lawyer apprentice) and I might need this if I want to get a job at a law firm.

So, how do you think it should be done?

Some basics:

Begin by explaining what your job is and what your boss’s relationship to you is. Then give some of the primary effects your work has had on the running of whatever it is that you do. Then show how what you have done, especially things that won’t really show up on your resume, demonstrates your qualifications for the thing you’re trying to do. Work in how your personality and perspective on life make you a natural fit for whatever you want to do. Finally, in a summary, really hammer the point home that you are awesome. Post-finally, have someone with some knowledge of whatever you’re trying to do look it over. There’s often a code of sorts to these things.

Some things to not do:
Don’t say anything negative about yourself. Or even imply it.
Don’t say anything irrelevant. It’ll seem like filler.
Don’t be vague. Give specific examples, with quantifiable details if your job is amenable to it.
Don’t make yourself to be a one-trick pony. Use varied examples of your awesomeness.
Don’t sell yourself short. If you can do something, say you can do it. Don’t say you can kind of do it. (If competence Z requires both X and Y, don’t say you can kind of do Z, if, for example, you’re good at X and not so good at Y. Rather, say that you’re great at X.)