Way back when (oh, say 26 months ago or so) when I was pregnant with the twins, one of my good friends gave me a gift. And as they say, it was the gift that kept on giving --- for the last 20 months.
It was a sleep training book specifically for twins, "Healthy Sleep Habigs, Happy Twins".
And besides my actual Bible, it has become my bible of sorts. I've pored through it numerous times, earmarked pages, re-read passages multiple times, and even prayed over it once or twice :) But this thing works. My kids are not angels, but they are darn good sleepers and have been since about 10-12 weeks old. Sleep was a precious commodity I couldn't afford to give up for very long. I get very mean and irritable and who wants to live with that? So schedule and sleep was critical for our family.
It does require some sacrifices in schedule --- you have to try to do your best to be home during all naptimes and you give up a lot to "keep the schedule". I think I may have been called a schedule Nazi a few times (I prefer A-type as opposed to the former). But our family needed that. And now they can be "off" for a little bit and fall right back in line. I was amazed how easily Q readjusted post-heart surgery. For over a month, she was not on any sort of schedule, unless you consider vitals at midnight and 4am, then an xray at 6am, a schedule. I don't. That child came home and immediately went right back to her regular sleep and nap schedule. It has been so ingrained in her that not even a month long hospital stay could deter that :)
And I really do think this book works for all types of baby personalities. Mine are about as opposite as you get and it worked for both of them. Anyway, for all you moms of singletons, the original version was for just one baby, "Healthy Sleep Habits, Happy Child". If you have a young 'un or better yet, have a friend who is expecting --- give them this book. They will thank you from the moment the child sleeps through the night to well, forever. I am still thanking my friend :)