Having an idea is different to making it happen, and usually we are better at one or the other.
You probably already know this about yourself: are you a starter or a finisher? An ideas person or a take-the-task-and-run-with-it person? The initial momentum or the patient follow-through?
Usually we are naturally one way or the other, so strengthening our skills in the places we struggle is one way to become a more effective person.
The other, of course, is to find someone else to plug the gaps. Need help with follow-through? Partner with a finisher. Need more ideas? Find a starter-up-er.
The first—and hardest—step in all of this is getting honest about your own abilities.