Next look for a rotating brush. A rotating brush will agitate the solution in the carpet and help break free the soil, and finally look or ask if you can add on accessory tools. Stairs and upholstery are very hard to do with out them. Now time, heat, agitation, and chemical are the four part equation to good cleaning. Time or dwell time is the amount of elapsed time between the time you applied the chemical and the time you removed the chemical.
Agitation is the physical act of scrubbing the carpets.
Chemical is either the dilution ratio or the ph. When you take away from one you must add to the others. Keeping an even balanced system. Using the deck sprayer properly mix your pre spray and spray all areas you wish to spray, starting with the farthest point and working back. Dwell time will vary but pre sprays can be left in the carpet as long as you wish, but don't let them dry, and as a rule of thumb 15mins is a good dwell time.