More than any other room, bathrooms have to deal with a combination of dirt, water and the many byproducts of human activity. As such, they also require the most vigilant attention for both cleaning and maintenance. Regularly giving some time to your bathroom will help ensure it remains in excellent condition for many decades.
Caulk/Grout: Your First Line of Defense
One of the best things you can do for your bathroom is to get as much of the water down a drain as possible. Allowing standing watereven invisibly small pools of itto infiltrate the crevices of your bathroom is just asking mold to overrun the place. This mold will appear innocuously enough, but can be a pain to remove and if left unchecked can cause serious and costly damage.
The caulk or grout that fills the spaces between your tiling is there to create a seal that repels water. If your sealant is worn or has gaps water may be getting behind your tiling. This is a recipe for disaster. If the problem occurs in a place where water can't easily reach, it may not require your immediate attention, but you'll certainly want to take care of it the next time you re-caulk or re-grout. As long as there are no problem areas, you should only need to caulk or grout once a year, but remember to go also cover the areas around your fixtures.
Shower Doors and Curtains
Even with caulking or grouting that is in good repair, there are still areas you should check for mold. The most common place is shower doors or curtains. The tracks of a shower door can be a perfect place for water to gather and even with properly designed holes it's difficult to get all the water to drain back into the tub. If you notice mold or a white filmy residue on your shower door or curtain, pull the door or curtain out and clean it with an abrasive cleaning solution. Your shower door or curtain can endure a lot of wear and tear so you may want to check this area out more frequently than the rest of your bathtub.
Bathroom Sinks
Bathroom sinks are often dirtier than kitchen sinks. They don't have disposals and are often see a wider array of items go down their drains. While a general cleaning of the sink and surrounding area is important, you should also pull out the sink stopper on a regular basis. Do more than just clean it off; the stopper should be soaked in vinegar and thrown in the dishwasher. This process can be necessary to remove the slime and any mold from the stopper. Check the faucet and the surrounding counter for evidence of any leaks. Keep in mind they may be hard to detect since water typically gets sloshed around this area anyway.
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Toilets
This can be one of the easiest things to clean in your bathroom as long as you do it on a regular basis. Have a cleaning brush nearby and it should only take a minute to go over the surface area of the porcelain. Every so often, you should also take a rag and run it around the base of the toilet. If you detect water around your toilet, it could be a sign that the seal protecting the floor from the plumbing is wearing thin and bigger problems are on the way. Also, lift the top of the toilet off and check to make sure everything looks right. Make sure the water level is consistent with the last time you checked, the flotation device is working and that nothing seems wrong. If something is amiss, call a plumber.
From Top to Bottom
Two areas of a bathroom that frequently get neglected are the floors and the ceiling, especially the exhaust fan. Your bathroom floor inevitably gets wet and this moisture allows all kinds of filth to stick to it. Bathroom floor mats are also a common problem. Thick and plush, these mats are designed to hide the water and filth they absorb and still get filthy more quickly than you would expect. Both your bathroom floors and your mats should be cleaned at least as frequently as any other floor in your home.
Even if it's inconvenient, you can't forget about your exhaust fan. Cleaning the filter, vacuuming the intake panel, and dusting the fan once a month will help the machine run better. 
Marcus Pickett is a professional freelance writer for the home remodeling industry. He has published more than 600 articles on both regional and national topics within the home improvement industry.