K.H.
If you do it when HE really shows an interest then you don't need any books , when he becomes curious of the potty or toilet , tells you that he has done/or needs to pee or poo then he is ready. What I have done with my first 2 (youngest not quite there yet) , is leave them with nothing on the bottom half & for the first few days stay home , take them every hour and sit them on to see if they need to go. The key is not to force them to train if they don't want to , when they are ready is really is quite a quick process.
Also night time dryness can take longer than daytime , it doesn't mean they are not potty trained though , some kids just cannot wake up in the night if they need to go. My middle daughter is now 4 , she started training at 3 and within a week was trained with pee and poo , but she still wears a pull up to bed at night and yes it is wet in the morning , she is such a deep sleeper I can literally lift her out the bed and move her elsewhere in the house and she will not wake up!!!