I commend you Jamie for the fact you have filled in your profile when joining clean it up.
Many dont and because of that others are reluctant to fully respond.
What do you do now for a living?
Why do you want to get into carpet cleaning?
Have you had any experiance of c/cleaning?
One of the best ways of getting the feel for anything is to go out with an experianced person for a few jobs.
Do you know any cleaners?
Maybe those close to you may be reluctant to do this because you may be a competitor in the future, but someone maybe 20/30 miles away may be approachable.
You can buy a half decent machine 2nd hand for around 1k.
2 vacs and 135psi pump is probably the minimum you need.
Training can be got from a number of places, most are linked in with a machine or cleaning fluid supplier so may be strongly biased. Or try
www.ncca.co.uk in Leicester.
Advertising can eat you £4k very quickly.
Websites can be done cheap but you need them high on the search engine rankings and that can cost money.
Leaflets can be expensive and you need regularity to get a decent response.
Local magazines can be rewarding and not too expensive - again regularity.
Knock on doors and sell yourself is a good way - but you need confidence and the householde needs to see this so they can be confident.
All trial and error.
You need insurance - public liability with treatment risk preferred.
Times are hard at the moment, starting up will not be a breeze. You need to think it out, plan well and ride a rough ride till you get established which will take years.