Get the items in order but if you are losing lane you can get (CQ) first before (ES) Try not to leave the lane (ER) and (ES) should be able to keep your health high so you can keep farming and spamming abilities
Get this if you are soloing and the enemy is very agressive DO NOT FIGHT, focus on getting souls Unless, there is someone there to help you for 2vs1 Dont buy (QS) instead buy (MR).
Get in order Depends on the enemy carry, if the enemy deals a lot of physical damage get (BA) Be careful on what you are selling Some of the items might be needed as a material for late game items
Get in Order However, if you need more physical damage go to the "OPTIONAL" sections most of the time you should be okay with these Put (SC) into your ultimate! its going to keep you in the fight longer