You should know how to clean and how often to do so.
Cleaning most rooms is often just organizing (though if you put things away immediately after use, you can avoid needing to do much of this at any one time) and a bit of dusting. Put everything in its place. If it doesn’t have a place, get rid of it or make a place for it. Dust solid surfaces with a slightly damp rag. Clear cobwebs from the ceiling.
Apartment Therapy has created a good schedule for cleaning. I think it’s a bit idealistic, but that’s what we should aim for. It’s not fun, but if you vacuum only once in three months (like my roommate and I did one semester) things start to look a bit unpleasant.
Bathrooms are even less fun to clean than bedrooms, but they certainly need it. My college cleans bathrooms for us once a week, so I don’t have to worry about it too much, but it’s a good skill to have when you move into an apartment or for helping out at home. And it’s easy, just a bit gross.
Clean toilet bowls by squirting toilet bowl cleaner around the inside rim and then scrubbing thoroughly with a brush. Spray all parts of the toilet (including the flush lever) with a disinfectant spray such as Lysol. Also spray the floor around the toilet. Wipe up the remainder after a while.
Don’t forget to clean the bathtub and/or shower, sinks, etc. You can find more information at HowStuffWorks. Don’t neglect this warning:
Before you clean your toilet, read the label on your cleaning product to learn its exact chemical makeup and how it should be used. Be especially careful never to mix products that contain chlorine bleach with ammonia-base products.
Mixing bleach and ammonia is dangerous: it reacts to release toxic chemicals.