Hi I had to apply by about November and I wanted to do it in July, for vetting etc. The other beneficial thing I did (not sure if your local force do it, but worth asking) was the youth mentoring scheme, in my area I believe they took about 20 people, including people who want to join the police and people who need guidance from them, me being the one who wants to join!!! For me this meant having some guidance on all the options available for me and going through them with a mentor, talking about unis etc. and routes into the police...this also allowed me to go on 6 hour shifts with response, allowing me to see the reality of policing, and also visiting police HQ in my area...this was for 6 months and was a thoroughly enjoyable experience