We live in a time when your 20s are basically a protracted adolescence, making it acceptable to spend that decade in complete squalor. By the time you turn 30, though, there are certain teenage-level habits that you really should've grown out of. These are some of them.
Not brushing your teeth before bed
You've known that brushing your teeth before bed is a thing you should have been doing since, oh, early childhood. But without mom or dad around to nag you, it may be a good habit you let go by the wayside somewhere along the way to adulthood. You really gotta pick that habit back up, even if only for vanity's sake -- as you age, your teeth will begin to yellow and develop ugly staining, especially if you're a regular coffee or tea drinker, or if you never managed to quit smoking. If an appeal to your vanity doesn't move you, how about an appeal to your wallet? Dental work is crazy expensive, even if you have good insurance.
Leaving your fingernails and toenails unattended
Your finger- and toenails should be three things: clipped, clean, and free of fungal infections. Use a clipper to keep your nails at a reasonable length -- clipping after you've showered, when nails are softer and easier to work with, can make that process a bit less of a production. A nail brush or orange stick can be used to remove dirt and grime from under nails. If you have a problem with fungus developing under the nail, use an over-the-counter treatment like Fungi-Nail; if problems persist, see a doctor.