The definition of "messy" is locked away in lexicons the world over, what differs is one's tolerance for said disorder. So, how do you recognise when your untidy habits are too much and more importantly, what you can do to address them?
Unclutter's Erin Doland decided to field such a question from one of the site's readers. Doland first covers off the more obvious points, for example, if you don't share you house or apartment with anyone else, you can decide what's an acceptable level of mess, as long as it's not infringing on your neighbours. On the other hand, if you do have flatmates, Doland recommends coming to an agreement on neutral ground:
There are lots of ways you can reach this agreement, but I recommend meeting in a public place (like a restaurant or coffee shop) and discussing it there. Write down the standards if that suits you, or simply come to a very clear verbal agreement. Remember, too, you can always revisit the standards you set at a later time if they turn out to be too strict or too lenient.
There's also the point when mess goes beyond a misplaced book or open drawer -- used plates, dirty clothes and other items of questionable hygiene should be attended to within a reasonable time frame, lest they become a larger problem by, say, attracting pests or generating interesting smells. Living the single life, it can be tempting to just let things sit for a few days, but you're just going to end up having to clean that much more when you do eventually get round to it.
Finally, if you're having trouble sorting out a regular cleaning schedule, Doland suggests a 15-minute "daily pickup routine" dedicated to cleaning up as much as possible. This time should be allocated when your energy levels are high and you should focus on the "little messes" -- things you'll be able to tackle in seconds or minutes. This keeps your cleaning restricted to tiny chunks so as long as you're not creating mess by the room-load, this routine should allow you to keep things under control.
Ask Unclutter: How much mess is too much mess? [Unclutter]