Well, some of those games cheat to get to the top using a paid service to download and even click the ads so I would not put a lot of weight on those numbers and I would not go that route as it is dishonest.
Some games get a lot of publicity from their own promotions on facebook and other social networks like Reddit but unless the reviews are legitimate and many are not again it is dishonest.
Some games go viral if they are really good and they usually have some unique mechanics not seen before in games like Flappy bird and candy crush used some unique mechanics.
So just focus on making a unique game with great mechanics, graphics and fun to play and then promote the heck out of it on all the social networks and hope for the best.