The best way to get started is to start.
OK generally you will think of an idea, now this may come at any moment in a dream, doing washing up, in the shower, out for a walk or on the loo well you get the idea. Now here's what you do.
Write it down!
Fantastic you've done that. Next work out what you need in order to get it done, the best thing you can give yourself is time. So set some time aside to get going with it, the sooner the better.
Give yourself more time than you need!
Okey dokey you've got your idea and the time to act on it; well done. Get doing, seriously just being. Once you get into a pattern of off putting or "I'm not ready" or "Am I allowed" that is where you fail.
Just do it!
On the thought of "Is my idea good enough" I say this "Do it, then find out" (if you know it's illegal, stop in your tracks) is a marmite cake a stupid pudding probably or a catalogued collection of your belly button fluff may be odd, but how do you know that until you've tried.
If you like it chances are someone ells will, so roll with it. At the end of the day you will have the work and your personal achievement.
One more thing if you have been knocking thought about I've left it too long I have not got started for months or years, bugger it! Yesterday happened who cares you can start today and go for it!
"But someone has already do it" so you don't think it is original that is fair enough it is original to you isn't it. How mush is that other person charging for it or what can you bring to what they have missed?
Do it for you first!