if you want 20 kills here goes the surefire way to get 20 kills.
First off, buy Agandaur, secondly you need to unlock a few relics and gems.
You need to buy Xp Potions, have xp potions in all 4 slots of your potion hotkey
In your first relic slot use the Relic that increases Ap by 14 with every Sapphire in your belt.
Put in all + AP gems, the higher the better, continually replace them with better gems as you save up Gold, It's called Seat of Seeing Relic
In your second relic slot, put the Relic that add a flat rate of 70 ap. Called Light of the West Relic, fill it with + AP gems, might want to include one Life Steal gem,
Third relic is Warg Claw Relic, again all +AP, might want to put in another life steal or an Penitration gem just incase you face lots of tanks.
Play on one lane here goes the way you get kills. First hit your teleport followed by your lighting (Don't use overcharge.) As you make your way toward the first tower wait until Teleport pops and use it.
You'll have three over charge gems. When you reach your tower rush into the woods, be ready to teleport out if you see trouble. Now your mission is to continually restock up on overcharge balls while firing up your AE lighting attack.
Use those Xp potions, You shouldn't put any points into Teleport it's worthless, start with lighting, Overcharge, lighting, overcharge, ultimate, lighting, ultimate
At level 7 you can start to kill people fairly easily. Continually hide in the bushes, wait till you see a large group of enemies in the mid lane, pop overcharge and blast your Ultimate.
Continually use this method until you push them back to their second tower. Here you want to hide in the section of bushes right by their shrine. Wait until your ultimate is up, overcharge and blast the ultimate toward the tower, hope you get a few of them caught up in it. Once it finishes teleport out before the tower downs you.
Use this method and you should pick up 20 kills, the better gems you have the easier your kills will get. if you are facing a heavy tank team hope your team works well togther.
Dont' be afraid to sit back and let the other team come to you. Rushing can be suicide.