If you know people those you what to be advisors, you should write them, show idea and invite to the project. Maybe you should visit some blockchain conferences, meetings and get to know smart people.
Also if you do not know anybody you should make announcement of the project here on bitcointalk. After you will start project and you'll gain some attention some of advisors will ask you to join
What watke me to make announcements in Bitcointalk for Advisors? Should be if I had a project website and a whitepaper is already dial-up ? or, you can draft about the project ?