Look for the easy solution first
Kathy wisely reminds us to check the obvious, low-tech solution first:
Our daughter Brigid just reached her three-month milestone. A couple of weeks ago, she started to flirt with the idea of sleeping through the night. Some nights she'd go five, six, or even seven hours on that first stretch, which was like heaven. But like all babies, not known for their consistency and predictability at this (or any other) age, she had other nights when it seemed she stirred every couple of hours. Those nights, she didn't even always seem hungry or wet when she awoke--she usually just needed to be held for a minute or two and calmed, then she'd go back to sleep (unlike me).
Well, this drove me crazy. I had to know what we were doing right on the days prior to the long sleeping nights, or what we were doing wrong on the nights when she awoke over and over for no reason. I enhanced her already-established bedtime routine and stuck to it, trying to give her cues that it was nighttime and time to sleep. I had charts. I had lists. I wrote down everything. Nap frequency and duration. When she ate, how many times per day, and how much per feeding. When we did tummy time and how upset it made her. How many diapers we changed. Whether we got any time outside that day or not. What her temperature was each afternoon and evening. EVERYTHING. I couldn't find a correlation, no matter how hard I tried or how far I stretched the gargantuan amount of data I'd collected.
Then one night when she was having a wakeful night, I felt the bed shake as my husband shifted around on his side of the bed. I looked at the bassinet (she hasn't quite moved to her crib yet...ironically, we've been waiting for her to sleep longer through the night consistently first) and it was shaking too. I had pushed the bassinet right up flush with the mattress of our bed when we'd gone to bed that night. I pushed it just a bit further away, giving it a little buffer space, and laid her back down. Well, she went back to sleep for a nice long stretch after that. Since I have been aware of keeping enough space between the bassinet and our bed so that our movements in the night don't give her a shake, she's been sleeping really well.
[Great advice, as long as you remember that sometimes there is no solution, especially when it comes to newborn sleep. Tangent: one of the biggest challenges for me has been knowing when there's a "fix" and when I need to just accept certain difficulties in parenting. It often takes a while before that distinction becomes clear. -- Ed.]