If you want real help with your head of department application letter ask you existing head of department or a member of SLT to read over what you have ALREADY written for the letter / personal statement and listen to their feedback. This way you will learn how to write one, just in case you don't get the job, or want to get another job or help a member of your team write their's. I've done this and it's the best decision I made. My deputy head has been amazingly helpful and I've learnt how to write my personal statement & application letter in a really clear way that emphasises my strong points. Therefore, I feel really confident about the application. I've also been able to pass on that help to my friend who's also applying for a new job. Surely, this is what we teach the students: learn from those who know, don't copy off them.