Inside the washer. There's probably leftover residue inside your washing machine from washing your clothes, as well as chemicals left over from your detergent or other cleaning solutions. Give it a good rinse by running an empty cycle with hot water and either a cup of lemon juice (for rust), white vinegar (for odors or if you have hard water) or bleach (for stains), then keep the lid open overnight to air-dry.
The seal on your dryer or frontload washer. That rubber seal is what keeps dirt and water inside and away from your floor, so it's a common place for dirt and mold to accumulate. After running an empty load of hot water, like in the tip above, spray the seal with a mixture of water and bleach and wipe down the seal, making sure to clean between the rubber folds.
Underneath the washer and dryer. Unlike the armchair in your living room, these heavy appliances don't get moved around much, if ever. There's probably a growing dust bunny making itself at home underneath your dryer right now. If you can't move your washer and dryer periodically to clean underneath, improvise with a long-handled duster or a swiffer pad rigged onto a broom handle.
Your dryer vent. Lint clogging up your dryer vents will quickly kill its efficiency, and create a fire hazard in the process. To clear out the clog, according to Wikihow, just unplug the dryer, remove the hose from the back of your machine and use a handheld vacuum to clear away any buildup from the dryer and the end of the hose. Do this deep-clean once a year and you'll be in good shape.
Your clothes iron. Mineral deposits and product buildup (from spray-starch or any other chemicals you're using) can accumulate on your iron, and probably almost never get cleaned off. Real Simple suggests applying a paste of baking soda and water to a cloth and wiping down the face of your iron with it. Then clear out the holes on the soleplate with cotton swabs.