If you use gravel in your tank (as many fish owners do), give it a weekly cleaning to eradicate fish waste, excess food, and other debris. However, there's no need to shut down or completely dismantle your tank in order to do so. The easiest way to clean gravel is with a vacuum made specifically for this process that can be purchased at your local pet supply shop. This tool involves a large hose that is pushed into the gravel on the aquarium floor, but the flow is strong enough to temporarily lift and tumble the gravel, which releases the more offending particles from the mix before returning it to its original resting place.
While we're on the topic of tools, other basics to add to your checklist include an algae scraper, de-chlorinating drops, and a skimmer net.