1. The dishwasher. It's not a magic food-dissolving contraption. It flushes dirty dishes with soap and hot water. If you put a plate full of food in it, the food will still be there when it's done doing its thing--only cooked on to the plate and much, much harder to remove. Because the dishwasher is not a trash can. It's not a garbage disposal. It's not made of magic. It does what it's supposed to, which is wash dishes. But you have to give it reasonable dishes to work on. Scrape that stuff off before you load your dish into the rack. It's what you're supposed to do. It's not that hard. Similar rules apply to the sink--if you don't have a garbage disposal (and most rentals don't), put the food you don't want in the trash before you put it in the sink. The drain catchers are there to catch small particles, not half meals. Don't be lazy.
Similarly, if you have a dishwasher, don't leave your dishes in the sink if it's empty. The sink is a waypoint for dirty dishes, not a final resting place. If you leave your stuff in the sink for more than a day you're kind of a jerk. (Admittedly, I've broken this rule. I'm kind of a jerk.) And if the dishwasher is full of clean dishes, don't just take the one you want out and leave the rest in there. Then it becomes unclear whether we're in dirty or clean mode, and mingling might occur. Empty it--it's fun! Like a game! You put the right things in the right places!--and go back to making your ramen.
2. Dishes. And pots and pans, and other communal kitchen stuff. If I bought them, they're mine even if I'm letting you use them. You're renting space in my stainless steel wok. Treat it with some degree of respect. Don't get scorch marks on my pans, don't put stuff in the dishwasher that doesn't go in the dishwasher (especially when it says on the bottom that it's not dishwasher safe), don't let things get so dirty for so long that I feel gross using them ever again. If you break something, tell me--maybe even pay me back a couple dollars. Don't leave me wondering. And don't keep my mugs in your room for months at a time. If you're not going to return them to circulation just buy your own mugs you can hoard. I need to get my green tea on.
3. Perishables. They go in the fridge--you know, that place that keeps the things you eat from getting prematurely disgusting. You're good enough at putting your food in there when you've just bought it. Why is it so much harder to put a head of lettuce back in the vegetable drawer after you make a salad? Not only is it wasteful, it makes our kitchen smelly. I know you have a very busy life but proper food storage is really not very time consuming.
4. Reasonable hours. That's awesome that you're the section leader of your a cappella group. Great job. I'm really happy for you. I'm not as happy that you and your unaccompanied buddies are full-on belting "Don't Stop Believing" at 9:30 on a Saturday morning. If you're going to sing and skip about with joy at least wait until it's a normal time for consciousness. If you're going to howl with laughter at something on YouTube at 3am--kittens are hilarious when you're drunk, I know--at least close your door first. Don't do it in the living room right outside the door to my room. It's Wednesday. I'm sleeping. And if you're going to power-clean--which you should if you leave beer bottles and taco wrappers all over the common areas on a weekly basis--try to avoid the temptation to do so at 8am on Sunday while blasting Li'l Wayne. I'm glad Weezy pumps you up. He can do that through headphones or perhaps at a later hour.
5. Laundry. It's not just for when you run out of underwear anymore. Dish towels and bath mats are very good at getting dirty and they don't clean themselves. Throw them in with your darks sometime.
6. Sharing is caring. If you make a big batch of delicious food and you don't share it and then it goes bad before you can eat even half of it you are a huge jerk. Forget kids in Africa; I'm hungry and poor and you just threw out half a pan of blondies because they went stale before you could shove all of them into your face. Next time I'm just stealing your food.