W first because with attack speed reds it clears faster (iirc), 2 points in E for the slightly better AoE waveclear, max Q for gank strength.
for items you want ancient golem for the health/cdr/tenacity.
From here you want CDR, Health and Resists. Check what the enemy team's damage type is and who is going to be a problem. If you need armor, get Frozen Heart, if you need Mres get Spirit Visage. You pretty much always want Frozen Heart by some point, the mana and CDR helps a lot in addition to the armor.
If your team has a lot of magic damage (Kennen top Lux mid for example) then you can grab an Abyssal Scepter to help them do more damage while picking up some damage and resistance yourself.