In general you dethrone companies by offering better or cheaper products. In the case of Google, the product is sold both to advertisers and to consumers so ea

In general you dethrone companies by offering better or cheaper products. In the case of Google, the product is sold both to advertisers and to consumers so each case should be examined. With regards to consumes, you'll have to offer better since you can't offer cheaper than free. But Google is motivated to offer better service so it'll be extremely complicated. One kind of potential better would make search so much better that people won't press on ads - which Google isn't interested in, so they might not offer such service, so you might have an opening there. Another option is to attack the adversity side :find a huge ads inventory and create a service more efficient and cheaper than Google. But that's extremely hard because on top of advertising space you need better data than Google.