I am currently applying for my chosen service which is the Royal Marines, I'm going talk to about stages you go through in recruitment. I would imagine for other services this would be the similar specially the armed forces.
Stage 1 - Deciding On a Service
The first stage is down to you deciding which service/force you want to join. Each of the services have lots to offer, all you have to do is decide which ones for you. Chose one you think you would enjoy, for example if you played a lot of sport the armed services maybe best suited to you as you'll be doing a lot of fitness and there are a lot of opportunities to play different sports. That's just an example I don't want you to think that because you enjoy football you'll be better off in the army because it also goes on your personality as well.
Here are the websites of the main Uniformed Public Services;
Emergency Services:
Police website; http://www.derbyshire.police.uk/Homepage.aspx
Ambulance service website; http://www.emas.nhs.uk/
Fire service website; http://www.derbys-fire.gov.uk/
Armed Services
Army; http://www.army.mod.uk/
Royal Air Force; http://www.raf.mod.uk/
Royal Navy; http://www.royalnavy.mod.uk/