I went to college at a fairly conservative place, and masturbation, though obviously a common activity, was hidden and not talked about. I had a little bit of a problem doing it at first, but then my urges got the better of me and I found ways.
My most common technique at first was to lay on my back with my knees up, making a kind of tent to hide my activity. I found that if I held my penis and rotated my hand around it, it gave good stimulation without the shaking that came with the up and down motion. The beds there had steel springs, so any shaking generated too much noise. I could keep up that rotating motion for about ten minutes, and bring myself to the point of no return. But no matter how hard I tried, the last few strokes were more jerky, and I couldn't resist the up and down motion that made the noise. So I learned how to move around as though I was turning over just as I orgasmed, so it hid the noise. I also had a hard time hiding my heavy breathing immediately afterwards, so I hid that by coughing a little. Then I'd wipe up, pull my boxers back up, and roll over and go to sleep.
I developed a better technique a little later. I'd Lay on my left side, and handle my penis the same way. It was more comfortable than on my back with my knees up, and I could bury my head in my pillow to hide the heavy breathing. I would have an athletic sock handy, and when I was getting close, I'd slip it over my penis so I could shoot into it, making cleanup much easier. And, with practice, I got better at not shaking the bed when I came, so I eventually could do it almost silently.
This is when I discovered how much more pleasure could be had from masturbation by going slow. I found the buildup to orgasm was much nicer if I didn't rush, and my penis would get so much more sensitive from a slow, gentle stimulation. In fact, I think I enjoy that aroused pleasure at least as much as the feeling of orgasm itself.
I had a different technique for times on weekends when I knew my roomate wouldn't be around. I'd get into bed naked, and pull the covers up. I had some shaving cream without menthol and other stuff that would sting my penis (you really have to be careful to not get regular shaving cream into your piss slit -- it burns like mad). I'd squirt some of that into a condom, put one pillow on top of another, and slip my condom-covered penis between them, and then hump in and out. It felt really great. The only problem is that I had to be careful that my penis didn't slip out of the condom, or my pillow would get all messed up with shaving cream. I'd thrust in and out slowly for as long as I could stand it. I'd stop every so often to back off from orgasm, then start up again. I could keep that up for about an hour, and when I finally gave in to orgasm it was all-consuming, and left me with a warm glow the rest of the day. And best of all, I had a neat little package I could just flush down the toilet, and cleanup was complete.
I remember one horny weekend when my roomate was out of town when I did that 6 times. I was exhausted by the time I finished the last one, but felt great for days.
I did witness my various roomates masturbating in bed at night on several occasions. It would always turn me on to watch them, but I never let on that I knew they were doing it. But I'd wait till I thought they were asleep and do myself, being aroused by the little I could see of them doing it. One guy was particularly brazen. He obviously thought I was asleep, but he was brave enough to pull his covers down, and I could see him stroking his penis and shooting his semen. He'd wipe up with an old cloth, and hide it under his mattress. I sniffed that cloth many times.
Only one roomate never seemed to masturbate, and he'd occasionally have wet dreams. I'd see him get up in the morning with a big wet stain on the front of his boxers. He'd yank them off and put them in his laundry bag and put on a new pair. When he left the room I'd pull them out and feel the wetness and sniff his semen. I felt guilty doing that, but it was a huge turnon.