Research your idea. See if there's a demand. A lot of people have great ideas, but they don't know if there's a need for it. You also have to research your competition.
“If you see most people neglect the Bible, and many that can read never look into it, let it not harden you and make you think lightly of it, and that it is a book of no worth.”
“Even in a time of elephantine vanity and greed, one never has to look far to see the campfires of gentle people.”