Q -> E -> W
Then max E first, Q 2nd, and don't put any more points into W until later.
Usual build path
Spellthief
Sightstone
CDR boots
Upgrade Spellthief to Frostfang
Redemption
Locket
Then upgrade to Frost Queen's
Ardent Censer is a really good item to get when it is late game.
Should be buying control ward whenever you can
Use auto to poke instead of using Q since you put only 1 point
Situational
Eye of the Watchers
Mikhael's