How do you make something great?
Build something that you can do today, this week.
Ship a little piece of it. Stop holding on to it. Maybe keep the idea big, but just start with something so small you can't not do it.
Make the smallest version possible. Give it away. Share it. Sell it. Tell people about it.
But start small. Make an MVP (minimum viable product). It's okay if you wince at the difference between your grand vision and your actual iteration. The first iteration can be improved. So can the second.
But only if you start.
Experiment. Play. Ask people to pay you money for it. (PS: it's okay to ask for money.)
What can you start, today?
What can you finish, today?
What can you ship, this week?