When you are in a concept stage then you should approach a mentor or a startup consultant who can help you in founding a startup after validation of the idea. Startup Consultants stay with the startup till the end from the beginning of the startup. Therefore you can discuss the idea with them and then start building the startup. After you get a good traction and consumer/customer base then you can approach the investors. Following are the steps that have to be followed before approaching the investors:

1. Develop an idea 2. Form a team 3. Validate the idea (with startup consultant) 4. Register a company 5. Start building the website/app 6. Start the operations 7. Promote the business 8. Make necessary changes for success of the business 9. Compare with the benchmark 10. Achieve the necessary traction After this:
11. Approach the Angel Investors 12. Make sure the investment will be used for expansion 13. The investment should not be used to buy Capital Assets 14. Get the Angel investment 15. Expand the business Now:
16. Ensure that you are in a revenue stage 17. Preferably the burn rate should be less than the run rate 18. Approach the Venture Capitalists 19. Pitch and negotiate the equity 20. Get investment for Series A Thereafter:
21. Continue to expand 22. Ensure the profits 23. Approach the Venture Capitalists again 24. Get the investment for Series B Repeat the steps from 21 to 24 for Series C, D and on, till you reach the IPO stage. In case you don't have the funding for maintaining an office and basic operations then you may approach an accelerator after the step 10.