describe your qualifications and experience
I recently had to appoint a new teacher, the main criteria the school was looking for was what else could that teacher offer, and many applications did not make the shortlist as they did not explicitly say what I was looking for. Applicants need to include the other subjects they are able to teach; NQTs should look at doing a secondary subject to improve their initial letter.
An awareness of current educational practice is good but do not write in great depth and waste time and space about it. Have a vision for after school or lunchtime clubs; something they have done or if an NQT something they would like to do, it could be linked to curriculum or an additional free choice, but they should look at school needs and try to offer something interesting and different.
Any previous work although unconnected to education can be phrased in such a way that it gives a sense of transferable skills. Most importantly, the letters should be spell checked and proofread. With a literacy agenda in school I disregarded three letters that were full of basic spelling mistakes and seemed rushed and were poorly written.