On carpet, use slow, repetitive front-to-back motions in an overlapping sequence. A quick once over doesn’t do much.  On the other hand, don’t press down or make too many passes over the same spot. Instead, move slightly to the left or right about every four strokes.
To get the most out of your vacuuming regime, remember these few easy tips:

• When vacuuming, don’t ignore those corners and crevices where dust builds.
• “Top-down” cleaning saves you the step of vacuuming again after dusting. Dust blinds, windowsills, and furniture surfaces first and then vacuum away any fallen dust.
• Remember to remove and replace or empty vacuum bags when they are half to two-thirds full.

Then sit back and watch this funny video!
How To vacuum a cat!