It is not enough to have a good idea. Your good idea must also be well positioned, or review panels for grant agencies are unlikely to approve it. Grant writing is the end of a process, not the beginning. Long before you make the decision to write a grant proposal for your research, you should be taking concrete steps to raise your profile in the eyes of reviewers.
What does that mean? Most basically, it means preparing yourself as a scholar, a researcher, and a grant writer in ways that will strengthen the ideas behind your proposal, demonstrate that you have the wherewithal to carry out your project, and enhance your ability to communicate what reviewers are looking for.
The following article from the Chronicle of Higher Education describes ways to become a successful PI: