Marissa Mayer at Fortune’s Most Powerful Women Summit this week with Senior Editor at Large Pattie Sellers.

FORTUNE — Earlier this week, Yahoo YHOO reported quarterly earnings, and while they indicate the Web 1.0 property still has a long slog ahead before its turnaround could be called successful, Marissa Mayer has investors excited. Indeed, the company’s stock is up over 100% since she started in July 2012.

But as Mayer explained this week at Fortune’s Most Powerful Women Summit, held in Washington, D.C., she believes there are actually just a few decisions a leader really needs to make, but “you need to make them perfectly.” Here are her top three for Yahoo:

A commitment to mobile

“I think Yahoo’s future is going to be mobile apps,” Mayer said. And she has the numbers to prove it. Earlier this week during the company’s earnings call, Yahoo disclosed that its mobile user base grew by 15% to 380 million monthly members over the last quarter alone. From an internal standpoint, Mayer fanned the innovation flames by swapping out the BlackBerrys BBRY still being issued to every Yahoo employee for Apple AAPL iOS and Android devices, which now dominate the global smartphone market. Basic as it may sound, the move makes sense. Says Mayer: “We call it dog-fooding … where people try the product they’re developing.”

Inject new talent

Mayer has also made a concerted effort to bring new talent to Yahoo. To wit, the company has hired 1,000 new engineers this year and at least 50 Ph.D.s since Mayer took the reins, a move that has prompted an uptick in interested applicants: Yahoo received 17,000 applications in the last quarter alone.

Buying Tumblr

Yahoo’s $1.1 billion acquisition of Tumblr certainly got the industry’s attention. Although the startup founded by high school dropout David Karp hosts 136 million-plus blogs, it reportedly pulled in just $13 million in revenues last year. (It’s been said the company is aiming for $100 million for 2013.) But Mayer argues her “big bet” makes a lot of sense, comparing the relationship between Yahoo and Tumblr to complementary continents — at least geographically-speaking — like South America and Africa: Yahoo’s demographic skew older, for instance, while Tumblr’s is significantly younger. As for Karp himself? Says Mayer: “He’s really in tune with the community he has.”