A key step in cleaning a couch is to first remove any hair or loose dirt on the surface. You can use a vacuum cleaner with an attachment to remove the crumbs and dirt. Cleaning hair is a bit more difficult ---you can either use a product made specifically for lifting and removing hair, like the Pledge Sweeper, or just improvise by using a roll of packing or fabric tape. The tacky tape applied to the couch surface removes hair and other particles that remain after vacuuming.
The next product you need for cleaning a couch is a steam cleaner. This is a device similar to a vacuum that has a hose and handle connected to a water source. Steam ejects from the handle killing bacteria and loosening dirt from the surface. Because you're using steam and not water, your chances of leaving moisture inside of couch cushions are slim.
Some people also prefer to use a standard carpet cleaner with a special attachment to clean the surface of a cloth couch. The cleaner injects water and a cleaning solution into the surface then removes it again with the dirt. Though it is an effective cleaning tool, it is a bit riskier when used on a couch since some of the moisture may remain in the cushions.
You don't need to purchase expensive or harsh upholstery cleaning products in order to clean a couch. You can use a simple solution of vinegar and water instead. Vinegar is as effective on couches as it is on carpets. Mix about five parts water with one part vinegar in a spray bottle and spritz it over the surface. Use a scrub brush or damp cloth to scrub the couch surface clean. Allow a few hours to air dry. The vinegar helps remove offensive odor from the couch --- the vinegar smell goes away after a few hours. This natural product is usually fine for any type of upholstery from cloth to leather, but test a small area for color-steadfastness before you clean the entire couch with the vinegar solution.