A clean vacuum cleaner makes a bigger difference than you'd think. Here's the most effective method, plus the mistakes most people make.
Always unplug before cleaning any vacuum components.
Empty the canister into the trash. For bagged vacuums, replace the bag if more than half full.
Locate and remove the filter according to your vacuum manual. Most have multiple filters.
If labeled washable, rinse the filter under warm running water until water runs clear. Use mild soap if needed. Never wash HEPA filters that are not labeled washable.
Let the filter air dry completely (24-48 hours) before reinstalling. A wet filter can damage the vacuum motor.