I'd recommend starting to develop the idea. If you are non-technical, then begin speaking to potential users and customers, and building relationships i.e. do business development.
If you are technical, it doesn't matter, do the above too. You can also take part of your time to actually begin prototyping a v1 of your product. But remember, your goal is to start a company, not a cool technical demo, so prioritize business development.
Once you have done this, congrats, you have some real momentum on your idea and have either gotten validation from real users and customers or know what needs to be changed and improved. You are now in a stronger position to start talking to people. Its much easier to attract people to your startup if you can demonstrate your idea has some traction.