There are 6 secrets to make it work:
Find a good Fertility Awareness Method coach. This is where I started - Boulder Fertility
Use a good period tracking app
Check your waking temperature daily. - Use this thermometer.
Check your cervical fluid several times a day.
Use protection on fertile days
A fertility awareness coach will teach you the basics and help you for the first few cycles until you are an expert.
To avoid pregnancy, the easiest way to check your cervical fluid is this.... if there anything in your panties (creamy, sticky, watery, egg white or dried up any of these)... use protection.
Be in health.