I think it is a number of things including traction, team and market fit. Most investors are investing for the long term and are prepared to invest in companies that have strong growth potential.
Today most entrepreneurs who haven't already successful raised VC funding and had a successful exit in their past need to have a product in place with paying customers.
In my experience with recent current funding trends you should focus your efforts on building your team, product and acquiring customers ASAP before contacting investors including seed, early stage or venture capital.
Paul Graham of Y Combinator gives a good overview of funding stages here:
Good luck with your efforts!