For that you might want to either get a book to use yourself in order to learn how to teach the rules, then turn around and teach your child, or something your child could use as well. It's nicely organized so that each rule is easy to find and very systematic. I'm not sure how extensively this book covers all the phonics rules. I don't remember. It's usually always worth going to see.
Children do their best learning when they are excited about something.
It is the phonetic approach in which students learn to sound out letters and syllables. I personally think the best time to teach it is when the child shows an interest in learning to read. Whether it be 3 or 6 or somewhere in between. Some do mature at different times, as I've frequently mentioned in my posts about my own children learning to read. My children have always seemed to learn their ABC's at an early age from their older siblings or when I'd play simple games with them.