First: sry, my english very poor. :)
Second: its my first guide, so im sorry for not finished yet and a bit hard to understand. :)

I like to harass enemies in early game to give a little time to breath for teammates, for this, im just going on the lane, hit once-twice the enemy and fall back to finish my jungle. But when enemy pushing hard any lanes, im just going there, and can get easy kills, coz WW never lower than full health. But the best way is: reach lvl 6 at same time like top lane, and can gank really quick. If possible, just walking to them, and giving attack speed, using hungering strike. when enemy looks want to quit the battle, then its time to use ulti.

Mark of Magic Penetration for hungering strike (very helpful at the early game as well as endgame too)
Seal of Armor: at the beginning, good against jungle monsters, and at any lane.
Glyph of Scaling Magic Resist: always need it. :)
Greater Quintessence of Ability Power: at early game (before lvl 6) help to make good damage, and selfheal.