The best advice for keeping your carpets clean is still pretty straightforward:
Keep the dirt away from your carpets in the first place. Use walk-off mats at the door, use indoor-only shoes or remove shoes while you're in the house.
Vacuum regularly. It's one of the easiest and least expensive preventive maintenance steps you can do for your carpet.
Have your carpets professionally cleaned when needed. Professional carpet cleaning systems are more effective than the do-it-yourself units. More importantly your carpet warranty most likely will require professional cleaning.
Take care of spills immediately! Preventing spills from saturating your carpet, using the proper technique and cleaners (when applicable) to 'blot' spills up will minimize the chances of permanent staining.