Watching for nap cues and paying attention to optimal waketime length.
At least, this has been true of the books I’ve read so far. I’m all for wearing Lydia most of the time during the day and co-sleeping with her at night, but after the first weeks where she would just fall asleep when she was tired right away no matter what (at least, it seemed as though that was what she was doing), I’ve found that the single most important thing I can do to make sure she remains happy is make sure she doesn’t stay up for too long of a stretch.
Against the recommendations of books like Babywise and the Baby Whisperer books, I’m fine with walking and nursing her to sleep, but I’ve found that it’s very helpful to start that process before she’s too tired, which can actually happen kind of quickly. I carry her a lot, but sometimes she’s having tummy time, or I’m talking to and flirting with her, or having her practice using her leg muscles, or pottying her. And these days she can’t usually fall asleep while I’m doing those things, so I run the risk of letting her get overly tired, at which point she’s upset and it gets harder for her to relax.
Our current rhythm is that Lydia usually has two naps that are about two hours long between around 9 or 10am, when we both get up for the day in earnest, and around 7 or 8, after which point I mostly encourage her to go right back to sleep after feeding if she gets up. That seems to work okay, and is getting increasingly to the point when it’s stable enough that I can actually schedule around it, which is also very convenient!