Hi,
Firstly I would invest in a decent machine ninja/steamway. Don't buy a second hand machine off ebay, I could sell you a 400psi ninja, via ebay, but its been well used/hammered, but you wouldn't know, see what I mean.
Leave well alone karcher puzzi.henrys. They give all professional a bad name, because you buy cheap, so you'll sell cheap.
Use good chemicals chemspec/prochem/one step. Don't be buying 5litres of carpet shampoo for £5 from the local engineers merchant, you customers will be calling you back, and it won't be to thank you.
I would get yourself on a course, however this is not always possible, if you are already running. Chemspec do a good manual on carpet cleaning, and if you buy from good supplier, John Kelly at Restormate knows his stuff then they will also give you advice.
Regards
Graham.
ps I cover the Wirral & Chester so you could be considered a competitor, but over the years I've seen carpet cleaners come and go, and I do talk to my competitors.