Locate your vacuum's user guide to determine where all of your machine's parts are located and how they can be accessed. This knowledge is always worth knowing.
First Things First
Empty your vacuum's canister or replace the bag as required. This will automatically add suction power to your vacuum.
The rotating brush is the part underneath the vacuum that rotates as the machine works. Clean the brush thoroughly and remove any strings and other debris that may be obstructing it.
Remove and clean the belt. Grit can build on the belt over time reducing its effectiveness. Wash, rinse and dry the belt before putting it back onto the vacuum. Cracks and signs of wear could mean replacing the belt.
Hoses and Filter
Inspect all of the hoses visually to ensure that none of them are blocked or clogged. Try to remove any blockages with a broom handle.
Rinsing or changing the filter regularly will also have a positive effect on your machine's effectiveness.