Look, I don't know how to make this guide look flashy. But I CAN tell you how not to suck with Illaoi.

If you are going against a ranged champ up top, like Teemo or something like that, then stay back behind your dudes and use Tentacle Smash (Q) to last hit minions for gold. Try to line it up so it hits the enemy too, but don't go too deep cuz you have 0 movement options.

Just Chillllll man. When you get your (E), then try to snag that when you can. You wanna play near your tentacles, because a good player will be looking to get them out of the game.

If you are going up against a Non-ranged Champ, like a Garen or an Ornn, your gonna wanna press the attack. The more often you hit E, the more annoying mini games your opponent has to play while you farm in peace.

By now you should have your (R). Eat those river fruits to stay in lane if your jg allows it. Stay as long as you can. If the enemy Jungler comes in for a gank and they are kinda squishy, then backpeddle to 1 or 2 tentacles, and WHAM. Hit them with the E. Then hit R and mash W on the ghost first. This should usually be a double kill if you aren't too behind. This leads heavy into the next part.

There it is! GITLSW! You have the tankiness to soak damage for your team ( provided they are present) So when the enemy team is bunched up, Hit that E on literally anyone, then Press R. That's HALF the job right there!
You're gonna wanna press W on all the squishies, ,and if they try to run away, or you are on cooldown.... then a Q doesn't hurt either. Even if you die, most of the time it is fine. Because either you got a triple or quardra, or the whole team is so low that your heavy hitter can sweep up the mess to get Dragon. The rest of the game snowballs from there. Be with your team, but make sure your teams is Getting in there....

LIKE SWIMWEAR.