Some D-I-Y tips

Select a suitable carpet, depending on the area it is intended for, the amount of traffic it's going to recieve and the surroundings. This will reduce the potential for problems later...
Frequent vacuuming prevents soil build-up: 3-7 strokes in the forward and backward direction with a good vacuum cleaner, but the last stroke should be in the direction of the pile for a smooth appearance.
TIP: Check out some useful information on vacuuming.
Clean-up any spills immediately!
TIP: Find invaluable tips in Interactive Stain Removal Guide.
Rent good equipment if you are going to clean the carpet yourself
Use good quality chemicals

Steps when cleaning the carpet yourself

Vacuum to remove as much soil as possible. It makes the cleaning operation much more effective.
Avoid getting the carpet too wet. Overwetting is at the root of many serious problems associated with carpet cleaning.
TIP: Check out the problems that can occur when cleaning your carpet!
Avoid using too much detergent: it might leave a residue that will cause excessive foam the next time the carpet is cleaned
Avoid applying too much carpet protector or deodorant: it might leave a residue that might attract soil.
Avoid using powder deodorant.