There's something called singing on an "ng" sound that's good for quieter practices. The idea is that internally you're doing all the right things, but what comes out is the volume of a hum. You sing the ng and it tends to keep your throat in the open position.
It's tough to describe, and if you tighten up your throat and don't sing all the way down from your legs, you could hurt your voice if trying to screatch out high notes, but it'a good quiet singing practice if you already have the basics of voice figured. I'd feel more comfortable with a teacher in the same room showing you that though.
These simple ideas are so hard to describe with text. Maybe someone has a youtube video of it. Take any vocal advice from someone not in the same room as you with a grain of salt though, including mine.
Edit - In Finland (or maybe it's just Helsinki, not sure), the official noise laws are lax when it comes to musicians. You can play for four hours nonstop before taking a brief brake, and then you can go on another four hours, and so on. Of course it's a monumental jerk that does this, that's why a trumpet playing friend of my father in-law's bought the apartment next to his, just to not make people angry. This was before the days of Silent Trumpet, which I don't know how well that works at all.
The guy next door to us is one hell of a blues guitar and bass player, but you can only hear him in the hallway. I'm waiting for him to come over here and correct me one day. In our old building, the guy above us, who we called Clumpy because of how he walked, would often drink until 4am, when he started what I call his Master P impression (a rapper whose sig is "Uhhhhhhhhh" in every song). Poetic justice was had in the mornings, by about 10:30, the guy above him was giving brass lessons to kids with the help of his piano.
That sound is so normal to me that I didn't even register it in my brain until I was installing a big huge new bed by myself, and ended collapsing on it. I stared up at the ceiling and realized I was listening to out of tune arpeggios. I smiled as I heard Clumpy groan. Payback's a bitch. Clumpy ended in almost burning down the building, but that's another story.
Clumpy was child's play compared to our next neighbor upstairs in the new place, Drunky. Drunky had a high level management job and a wife and kid and dog. Things were normal... until they had some bad fights and she moves out. Then started his 4 year long Lost Weekend. Any other house would have kicked his insane alcoholic butt out, but he skated by. He did loose a fair few jobs and threw tantrums before having to see his kid. Now he's working in America, drinking Texas dry. Good luck finding a liver. He's got tenants living here that are absolutely normal people, but we live in fear of his eventual return. 911 is a joke in yo town was written about Helsinki.
The best way to revenge Drunky was with the recorder. That high treble really cut through his hangovers. But he should have thought of that before starting his own personal rave at 5:30am, and then jumping up and down on the floor and telling us to go frak ourselves (not provoked, he's just mean).
It's nice to have normal people above us again.
So basically my little novel here is that people are cool to a fault when it comes to noise around here, but I try to not be a jerk about it. I suck anyway, so I try not to have too many people have to listen to that.