IF YOU HAVE THE OPPORTUNITY GO ON VETSIX AND VETSIM!!! I am at Vet School now, and sooo many people I've spoken to here went on it, learnt from it and subsequently got offers and places at Veterinary School.
Vetsix is just before Christmas, is the most useful in my opinion regarding applications, gettin offers, what to do if your A Levels aren't great etc etc etc. There are also lectures on animal husbandry and vet related stuff which can really give you an insight on what Vet School is all about. You can take an extra pathology day where you are given a subject and write a research report on it, which is then PUBLISHED if it's good enough - do it, it looks fab on your UCAS form.
Vetsim is in July, is much more hands on with fewer lectures. You get to play with llamas, reptiles, chickens, horses etc etc and play with your stethoscopes (provided). You can have a mock interview from someone who KNOWS WHAT HAPPENS (i.e. not some random English teacher who gave me a mock at school).
Its expensive, but ask your school if they can offer some help - there may be a bursary scheme or something. If you can get on this, you get so much advice and you get to see what/who you're up against. With 7+ people applying for every veterinary place you need all the help you can get!