When playing Evelynn placement and vision are key. As Evelynn your job is to power farm to 6, ganking when you get the chance and stop the enemy from getting ahead.
Control Wards are Evelynn worst nightmare, if there is an enemy control ward, ask your team to immediately kill it before ganking. If your allies cannot, do so yourself and look for another gank opportunity. It is difficult to give kills as Eve due to her large burst damage, but if you thin k the kill is secure, charm and only use Q to give your laner the kill. If you are not fed or do not have Dark Seal or Mejai's, DO NOT give them the kill. As Eve you are the hyper carry, if you cannot assassinate the enemy carries you are of little use. Do not go for risky kills unless the dives are worth the risk, Example: To steal Baron, Elder, or the Soul Dragon.
Be smart. Be safe. Be Sneaky. You are Evelynn.
-Weary Samurai