I read this book first while very sleep-deprived and then re-read
it later when not so wiped. It helped us enormously. The earlier
you read it, the better because it helps you put your baby to sleep
so she can learn to fall asleep on her own (not be rocked to
sleep).
The second most important thing I learned was how to recognise your
baby is tired and to put her to bed, for naps and the night, before
she is overtired and cannot fall asleep easily.
There are many more important things I learned from this book, too
many to mention here. I cannot recommend this book enough.