Lebonk is all in the combo. Go onto league, on the mainpage, and look in the bottom right at the games. there's almost always a lebonk playing. watch the game, and every team fight watch it, then go back and watch it @ 25% speed, focusing on her. watch for
1: pre-fight position. how far is she from the action, and where is she in relation to her team. off to the side? behind the tank? it all depends.
2: who she targets. target priority is HUGE on lebonk. know whose fed, and who has a good team fight. and
3: which combo you're doing. do you have time for the double E? do you have sufficient damage, and can afford the AoE from a double W? watch how the pros decide. and
4: watch the 'holy eff he just escaped that' because damn, they do that well in ranked games.
When you begin to understand and can predict when lebonk is gonna go in, and who the target is, then you've got a good start, then go practice! spam the champ. bots, normals, urf, dominion, whatever. play her till the combo is natural.