What would you like to know? I've been in school admin since 2006 (minus the career break for the kids) and have worked my way up and now hold a senior position in the school I'm currently in.
Generally the pay isn't particularly high. The job may advertise with the FTE (Full Time Equivalent) salary. Most admin roles are pro-rata meaning that you are only paid for 39 or 40 weeks of the year, plus any holiday allowance. This is reduced further if you do not work "full" hours which are usually 37 per week (36 in London), be aware of what the actual salary is, so that you don't get a nasty surprise.
Expect to work extremely hard during term time, you don't go into school admin for a quiet life. It's a fantastic environment, which I love, but everyone is exhausted by the end of every term and all school staff thoroughly deserve their holidays.
When recruiting for new staff, experience in similar environments is helpful. This could also include any volunteering with agencies or companies that work with children such as youth groups, brownies, summer camps etc.
Often only senior admin roles require specific qualifications, most ask for a minimum of 5 GCSEs and evidence of post 16 study. Any relevant qualification would be a bonus but not expected.
Brush up on safeguarding as you will be asked about this if you get to interview.
Schools often get lots of applications for admin jobs and anything with spelling mistakes, poor grammar or that has been handwritten is not looked upon favourably (this is due to most admin roles requiring a decent level of computer literacy and one would question why the form hadn't been filled in online and emailed in).
Make sure that you answer the person spec fully in any applications, giving examples of your skills from your previous experience. When shortlisting applicants, the person specification is used to grade applications, so if someone has only written in their statement that they want the job because they like kids and want a term time only job... they won't get shortlisted against others who have given examples and evidence of skills and experiences required. A recent job I was on the interview panel for had 20+ applications and we shortlisted 4.
In every school I've worked in, CVs are not accepted in place of the official application form. This is to ensure transparency in the recruitment process.
If you are looking for an admin role in a school, most schools advertise using eteach or TES jobs as well as on their own websites.
Please let me know if there's anything else you'd like to know.