i used to have very bad insomnia. I also work nights 2x per week and long shifts. Now, I sleep 6 hrs on my long shifts (purely because of no time to sleep more) and on days off i sleep 7-8+ hours. And i had BAD insomnia.
Light regulation is crucial. At the end of my shift i wear blue blocking glasses. You can go on amazon and research this. Buy the sunblock + blueblocking kind for the drive home. The regular blue blocking without sun blocking can be used on days you dont work.
Thats another thing - you have to stabilize your lifestyle patterns. You can NOT live in the daytime anymore if you accept a night position. Every day you have to sleep approximately the same time. Iin my case, on my long shifts i hit the bed around 7:45-8am. On day off work, i sleep at about 6am. I never ever live in daytime and every day i wake up at 2pm. The stability of patterns is as crucial to maintaining a circadian rhythm as light control.
You know to keep room dark which is good, but is it REALLY dark? I have 3 layers of black out curtains. I have a red curtain, a heavy brown curtain, and a normal blackout curtain. My room is dark when all the shades are drawn, literally black.
Waking up at the same time every day, like going to bed the same time every day, is crucial. As stated, I wake up about 2pm, every day. My body does this naturally now, buti also use a sunrise alarm to assist on work days when doing shorter sleep/longer shifts. Upon waking make SURE you see very bright light, especially important in the dark months as a nightshift worker because the sun will start to set sooner than you can go out to see it to program your body rhythm. So, you will also need to buy a light box. Super bright light upon waking, as in a light box, is just as important to cement your circadian rhythm, as the regular wake+sleep times, and the darkness while sleeping.
Finally, there is meds. I use low dose seroquel, which has helped extend my sleep from 6 hrs to 7-8 hrs. Almost all people find seroquel to be like MONDO for sleep. However, i bet if you do the above protocol I describe you probably won't even need it.
The bottom line is, if you are night shift, you're NIGHT SHIFT. You cant ever live in day, not even on your day off, not even because you want to go to lunch with your friends. It will royally mess your body regulation up and you will never sleep.
Night shift can be done but it takes a big commitment to controlling light and sleep times like a nazi. Most people are unwilling/unable to do this and just end up sleep deprived forever.