Lot's of good advice on here and the only thing we'd add, would be, not to use the full power, full heat more chemical applications than necessary, unless it's really justified.
In most cases, you will only require a moderately applied prespray, followed by aggitation, which can come from the powerfull jetting action, of your machine.
In most cases, you won't even need anything in the return tank, but an acid rinse, in moderation acts as an insurance .
Most of all, take it easy, remember, you can always go back over the carpet, if you're not sure of the result.
Best of luck
Angie