Start out with ninja Tabi to give more attack speed. Since xbal passive gives power don't worry about power to much early game.
Bloodforge should be next with bonus utility qualities
Fatalis is perfect for securing run away kills and giving more attacking speed and movement
Crit is nessesay so.deathbringer is your best option for burst damaged
Brawlers beat stick is really good on xbal as it provides extra pen and it's passive works well with the dots from poison darts
Finally executioner is your best bet or ichival for extra attack speed/ pen