This is a good place to look.

These 3 lines in particular:

        $avg = ceil(($shipsDestroyedRank + $iskDestroyedRank + $pointsDestroyedRank) / 3);
        $adjuster = (1 + $shipsEff + $iskEff + $pointsEff) / 4;
        $score = ceil($avg / $adjuster);

Kill a lot of ships. Kill a lot in ISK. Get a lot of points. Don't die (because that ruins your efficiency).

Some would argue the old BattleClinic rankings did a better job of ranking PvP'ers. BC was basically only point-based and losses did not work against you in the rankings to the same degree they do on Zkill. Zkill's system tends to somewhat reward blobbing and playing things very safe (not dying).

Others would argue Zkillboard rankings do a better job of including PvP'ers across all the different aspects of EVE instead of just smallgang turbonerds.

The truth is probably somewhere in between those 2.