I just looked at the DSPS section since that is my problem. The "I have mathematically proven this to work unless it is your fault" thing is really obnoxious. I've even tried his ultimate "farmer's lifestyle" suggestion that worked for about a year and then stopped working. Similarly, I've done things like bike around all day then relax without much light in the evening (all after getting less sleep than usual the previous night) all to spend over three hours in bed before getting to sleep.

For me, transdermal melatonin patches have been the single most helpful thing that actually improves the quality of my sleep, which seems to be my main issue (I cannot get good quality sleep even if free sleeping on the shifting schedule). I've been using them (on and off, since I try to use them only when sleeping at night) for a few months now and they aren't magic but do seem to help significantly. Other forms of melatonin, including extended release, have been able to slightly decrease my sleep onset but at the cost of waking up early (about 4 hours after I go to sleep I wake up and can't sleep again for at least 3 hours) and they do not improve my sleep quality.

Diphenhydramine, even 25 mg or less for weeks at a time, can help me get to sleep but does not improve sleep quality. I don't think it seems to make it worse either. For most people it stops helping with sleep after a couple of days, but for me I can notice the effects for at least a month and sometimes two (and just a couple of days off can make it effective again). I'm not sure how much of this is due to my allergies, which do seem to interact with the circadian rhythm issues.

Transdermal melatonin seems to decrease my sleep time and leaves me feeling more rested. Hopefully this continues and I eventually make up from a really gigantic sleep deficit :/. One point the author covers but could be emphasised more is that the time you wake up (and potentially but not exactly when actually get out of bed; for me it is easy to tell the effective wakeup time: that is when my allergies kick in) controls the time that you are able to get to sleep. This took me many years to really understand. I'm starting to wonder if the fundamental cause of delayed sleep phases might be related to sleep quality (that is, when quality is sufficiently low our bodies tend to sleep a little longer, but the time from waking to being able to fall asleep doesn't change).

I don't drink alcohol, but on the caffine topic I've noticed that for me caffine (well, theobromine at least) seems to accumulate in my body very slowly, but over weeks of daily consumption even in the morning it will start to affect my sleep. I find it easiest to avoid almost completely.

For me, the longest I've been able to stick to a fairly reliable schedule is three or four months at a time and involves spending at least three hours in bed before getting to sleep almost every day (and twelve hours in bed total most days). But it is still quite easy to get off that schedule, only partly due to the difficulty of spending that long in bed every day. On the plus side, I've found that my schedule can actually vary quite a bit day to day while on that general pattern and still be ok, so I don't think it is really a matter of being perfectly strict but of avoiding those situations that cause the most harm (e.g. it seems that staying up a few hours later than usual can be ok once a week or so but more often and it can cause the shifting to start again).

ETA: Learning to better recognize when I've actually woken up has been one of the most helpful things to me and took forever to recognize even with the allergies to help. It is very tempting when I haven't gotten much sleep (and it is 4 in the morning or something) to try to get back to sleep, but once I've passed that point I can almost never get to sleep again until at least 12 hours have passed. However, if I stay in bed the effective wakeup time in terms of getting to sleep in the evening can be pushed back, and even more so if I eventually do fall asleep again.

Another odity that I've noticed is that I get much more restful sleep when sick for some reason. I think it may be due to the rapid sleep stage cycling, since there is some other particularly restful type of sleep that occasionally happens in the morning.