Dorm / Hostel: How to assert myself politely with roommates

I occasionally travel with agencies that will put me in a dorm room with one or two twenty-something year young students for three weeks straight. Though day program is tough, some of them like to party late, sometimes even in the dorm.

Therefore I'd like to ask, how I could politely communicate my needs like

• No smoking in our dorm room.

• Try to be silent and keep lights low in our dorm room after 11pm.

• Don't use my stuff without asking - and if I answered no, don't ignore that.

• Ask before the fact when you need the room for yourself and don't just lock me out, etc.

I'm looking for ways to do this right at day one, as well as just before / while / after an unexpected negative encounter.

Note: I usually offer more money to get my own room, but sometimes it's unavoidable. Hotels are usually not in the vicinity, hence not quite an alternative.