There are two ways to approach it. the basic idea is get as much media surface area as possible, while still being able to fluidize the media 100% during a backwash (running water backwards thru the filter, but out to a drain instead of into the tank). The idea is that as the water goes from top to bottom, the debris you are filtering out is stacking at the top. After awhile, the junk prevents water from flowing into and out of the filter. So it's time to clean it. Some like to use tank water to backwash - which gives you a water change at the same time. Others like to have an outside water source (like city water) to backwash with. This means you aren't wasting your cycled non chlorine tank water to clean your filter. I like to do both. It allows more frequent filter cleaning without dumping large amounts out of the tank. But when it does come time for a water change, it's easy.
Some of the 'old school' sand filters are or domed. They offer great surface area and fluidize very quickly, making cleaning easier.
As far as how often you backwash, it really depends on bio-load. This is one reason why I always over size my filters and pumps. It just makes it easier to work with down the line. We've got some systems now that need major backwashing every other day. If they don't get done, the pressure builds so high that the seams leak.