I am a potential private parent.
As well as exam results, information on next school at 11, University destinations including Oxbridge and what subjects they are going to study (gives some idea of the school's strengths).
Information on the teachers and some insight into the lessons in the younger year groups is helpful.For older year groups the extra GCSE/A level options available such as extra languages.
At younger ages the smaller class sizes and nurturing individual attention is what I would be looking for and in the older ages the education opportunities including what the children go on when they leave school.
Information on the specific opportunity that may not be available in the state school. Sport,art,science showcasing the facilities and visitors to the school and pupil's work in a newsletter.Something such as a piece of art work or poem written by a child at the school if you have a child who has potential makes you think of the potential of the education available.
All parents want to know whether the school is a 'fit' for their child so the more information with lots of photos with children helps.
Increasing donations depends on the sense of belonging so perhaps a old ....'s for ex pupils at which they have the opportunity to meet up at the school a couple of times a year and regular newsletter on the school's achievement.
Present parents I would feel respond best to a specific need fundraising for a specific project which may benefit their child.
I'd look at as many private school websites as you can and send off for their prospectus as a potential parent which often includes other things such as newsletters.
I'm still thinking myself.It is a big commitment bearing in mind the present financial climate and the fact I want to pay my children's university tuition fees for them as I left without debt when I attended university.
Good luck with your job application.