depends on the filter,flowrate and bioload as to how fequently you clean it. for example my eheim 2217 can be left alone for 3+ months my xp3 about a month and my ac 110 I clean the sponge once a week.
I clean mine every six months... would just rinse the bio media in tank water and thoroughly clean the filter mats (mechanical filtration) with tap water... if the filter mats are too dirty I would replace them...
I clean mine whenever I notice that the flow rate is significantly lower. If you have a lot of gravel/sand sifting fish this will probably be more often because they turn over the gravel a lot making gravel/sand cleaning easier, but it is more work on you filter. For instance on my tank that I have tinfoils and 1 giant goldfish in I have to clean the filter out about every 2-3 months, but for my other tanks it is more like 4-5 months.
If you want to keep up on your carbon though you should probably do it more often since the carbon gets "used" up.
dang these maintenance times are off the hook!How often are FX5 owners cleaning out there cannisters?I'm cleaning out my cannister about every two weeks.