- Higher GRE/math scores
- A more prestigious undergraduate institution
- A reference letter from a prominent researcher
One of my colleagues once told me, "UP, if you're really smart and work hard, you'll publish a lot in top journals. If you're not quite as smart and you work hard, you'll still publish a lot, just in lower tier journals). Either way, if you work really hard (and intelligently), you'll publish a lot.
HT: Newmark's Door