Before EverFrost; In Early Pre 10 Laning Phase.

So the best way to engage, is Q W. Place your box in their path where they try to back away, and then try to get your crit from behind.

After Everfrost; Post 10-15 Laning Phase

NOW WE ARE GAMING! Your engage is now going to be Q W Everfrost. Easy kill in lane with your ADC.

How to Play Laning Phase

Level 2 is where it all begins! As soon as you get lvl 2 you can Q W engage.
But this isn't all you should do. Placing boxes around is important: bushes, edge of river and what not. NOW! These boxes should be placed based on how wave is, and your/enemy positioning

Wave Reset

Place boxes in the lane bushes, edge of river and edge of walls near river.

Wave Pushed into Enemies Tower

Place boxes in the edge of the river to avoid ganks.

Wave Pushed into your tower

So if you see they are pushing into your tower, place boxes beforehand in the bushes, or on the bottom side of the tower.