The one factor: meet a need. If you're selling something, make it something that people want at the right price and make it easy for them to buy. If you're se

The one factor: meet a need. If you're selling something, make it something that people want at the right price and make it easy for them to buy. If you're selling advertising (you're a decade late on that one...), give people a reason to come back to the site - make the site sticky or have network effects. Scaling comes later (assuming your initial design isn't a complete resource hog). It literally follows the money.