There are like a million sleep books out there. Probably you have  already read some and tried different sleep methods. As a Gentle Sleep Coach and Therapist I encourage you to find what works best for you but most of all to be consistent in whatever approach you choose. 
If you want to know a little more about sleep, age expectations around it, managing naps and get an insight on “The Sleep Lady Shuffle”  this will be a handy reference. 
This book has some basic guidelines at the beginning and then is broken down by age, so you don’t have to read the entire book. You can just flip to the sections that are relevant to your child. You can find it in kindle, nook or physical version.
The Author Kim West is a world-renowned child sleep expert who has spent 20 years teaching families how to reclaim their sleep. Her book has been published in 4 languages, and she has sold 100,000 copies in 13 Countries.
“Reading is dreaming with open eyes” ENJOY