The Baking Soda and Vacuum Trick
Baking soda is a natural adsorbent, which means it has the ability to absorb odors when used correctly and will help you learn how to clean a used couch. If you have fabric-covered furniture, then put some baking soda in a salt shaker or similar dispenser and sprinkle it liberally on the furniture you want to freshen up.
Baking soda doesn’t do its work all at once, so give it time to neutralize as many odor-causing particles as possible. An hour or so is ideal, and for bad situations, you may just want to leave the baking soda on overnight (as long as it won’t get tracked everywhere by pets). When the time has elapsed, get out the vacuum cleaner and thoroughly vacuum up all the baking soda. This should freshen up most fabrics.
Note: Baking soda may have varying effects based on what is causing the odor or general “staleness” of your furniture. It neutralizes acidic compounds very easily, but may not be effective for all problems.