Voted for All of the above.

Maybe all of the above, but the lamp doesn't really affect (or at least doesn't disturb) me.
The same goes with the natural light. Sometimes I sleep (or rather I slept) during the daytime. I had good sleeps. The lamp and the light is not a problem for me.
The good environment is certainly important. A noisy (and other unpleasant) environments can distrurb you during sleep.
The reducing the use of the smartphones at night can be a good idea, if you use a smartphone a lot during the night, and you have to sleep during the night.
I very rarely drink alcohol. Caffeine can be found in some desserts, but I also very rarely eat those. I don't drink coffee. I tried coffee (for example Cappuchino) a few times, but that is all.
Try to sleep at certain times is that is what we do. We usually sleep at night. Sometimes during the daytime. I often found myself sleeping in the daytime in the past, because I sat in front of the computer/laptop during the night, but nowadays I have a 4 hours part-time job during either before noon or afternoon, but mostly before noon.
Trying to sleep at certain times can be good. But "sleep, when you like to and/or need to sleep, when you feel it is right and/or necessary" can also work.