Cleaning is really needed when it's needed - there's not any particular schedule, but if you start seeing dust spots, and they're getting annoying, time to clean!
If you want to scare yourself a bit, simply set your camera to Aperture priority mode, dial the aperture down to F14-F22 or so, and take a photo of a blank white wall or neutral expanse of light color...that will show you pretty much all the dust that's hiding on your sensor. The smaller aperture reveals more of the dust that sometimes doesn't show up.
Easiest cleaning method is a bulb blower, commonly available for DSLRs - it's relatively cheap, super simple, and doesn't contact anything so less chance of damaging anything if you don't know what you're doing. And it works about 80% of the time, or more...so it's often all that's needed. Otherwise, you can get into using sensor brushes or wet swab systems, but those get a little more expensive and also involve a little more care on your part as you're wiping on the sensor's cover directly...if worried about this type of thing, there are usually camera shops somewhere in most cities that can perform it for you for a charge...or you can just get friendly with someone else with a DSLR that knows how to clean, and buy them a burger for lunch if they'll do it for you!