My brother and I, we share a room, have not had a good track record of keeping it clean. Usually he gets a cup of water before bed and leaves it somewhere in the room half full. He also never makes his bed. He's also very sentimental, so anything my parents intend to throw out that he deems worthy enough, he stocks it in our small room. This leaves our room cluttered, and hard to maintain. I have other issues. I usually leave plates because we don't have a bin and forget about it. I also sit on his bed a lot (doing homework or on the laptop), since mine doesn't have a comforter as mine slides out from under his to save space. Anywho, when it comes to cleaning the room usually it's me who steps up (after a fair bit of procrastination) and I do it when I have the motivation. This makes me super efficient, and I deep clean the room and straighten everything the best I can.
I have straightened out my recent lack of motivation in keeping the room clean and other aspects of my life. I acknowledge my problems and past experiences with this issue. I recently cleaned the entire room, and intend on keeping it entirely clean. The cleanliness has sparked productivity within me, but my brother's issues are still prevailing. I come home from school everyday to his bed unmade, his blanket on the floor, and wake up to a cup on the windowsill. I'm worried if I don't account for his issues in keeping up with the room that it will return to the pigsty it previously was. I have tried to address this issue to him but every time I do, he doesn't take me seriously, switches the subject, or says "But you make the room dirty with all the gross stuff!".
What are some things I can say to him? I don't want to come off completely assertive to him because he won't take it seriously if I start off like that. I want to segway into this at an oppurtunity I will find, but I just don't know how to express myself without him finding a way to ignore it. But if there's no other option I would like some things to say, where I am assertive. Just some things I can say to him at varying levels of intensity while not being rude or ignorable. Thank you so much!