I rang up to ask whether they do work exp. and who I'd need to address a letter to.
I included this:
-- my name, age, that I am studying a levels at ____ college/VI form
-- that I need work exp. for vet med course
-- what +ve qualities I have which make them allow me to do work experience
-- that if they would like a reference from my school tutor I can provide that upon request
-- what dates I'm available
-- contact details
-- CV which included all GCSES, current subjects, predicted grades, employment status, date of birth, my address/mob. number, personal qualities, list of achievements and certificates
Most did not reply to me. Sometimes I rang them up and politely asked if they got my letter and that I hadn't heard back from them. Normally then they would say they can't offer within those dates, but would offer me if any other dates were ok, or would give me a place straight away after they realise I was being serious about getting a placement there.
Good luck and be prepared for rejections!