Price: ~$20 per gallon
Materials needed: Paint, paintbrushes, good music, beer
Approximate time: Depends on size of room, how much beer you drink
So you've got four white walls and a dim flickering light sending an ominous glow off your eggshell-colored ceiling. If you aren’t an admirer of the mental institution vibe, throw a couple layers of paint up (ask your landlord first, though). It's instant gratification, and if you’re conflicted about what color to go for, check out this great app that will show you what different colors look like in different rooms.
10. For God's sake, get a new toilet seat
Materials needed: Toilet seat, screwdriver
Approximate time: Five minutes
Toilet seats are, by nature, indescribably boring and kinda gross -- especially when it's not yours. You sit on them. Sometimes leave them up. Sometimes put them down. Sometimes pee on them. But throwing a custom one in your privy can really go a long way, and they usually aren’t that expensive (unless you want something not-gaudy-at-all, like this guy). Also, it's just two screws to remove/install. Approx time: one minute.