I'll try and keep this guide short and simple, as it is my first. It is for aggressive play and intended for S marks and low elo climbing. Please comment and I'll try and check them.
Quints - Flat AP
Glyphs - Flat AP
Seals - Flat HP
Marks - Hybrid penetration/8 , Crit Chance/1
I run 18 in cunning with precision over intelligence. Then 12 in Resolve using Runic Armor.
Frostfang/boots/SS. Rush Ardent Censor. Finish EoW. Finish Sorc Shoes. Rush Lich Bane. Items beyond this point are of preference I suppose. I build a Haunted Guise and Large Rod, finish Rabadon's, finish Liandry's torment. At this point one can sell the EoW depending on vision status and build a Rylai's, Luden's, whatever...
Unlock Q/W/E. Max Q first. If your ADC is competent I advise putting spare points into E to help his kill pressure. If not put spare points in heal and poke them down until even a mongoloid could finish them.
During lane always keep just out of reach of the adc until Q is up. When approaching, if the adc goes to counter you heal first then cast Q so your shield absorbs his counterattack and your Q lands. Always make sure to follow your Q with an auto attack especially if your passive is ready to proc. After the AA back away and if they chase is heavy make sure to press E first. Ult wisely and sparingly and always...almost always...ult the adc. Then Q him and AA, then press E and run away giggling like a schoolgirl while your adc mops up.
If you aren't always just out of harms way and very aware of positioning and the minimap you will go 1/13/7. Also, minions hurt a lot with no armor.
P.S - Always spot a kill your adc will surely miss but you won't with your ridiculously ranged Q's and AA's. Take them, it is not ksing, and the opportunity arises multiple times in a game.