Engaging at the right time

Numbers, cooldowns, their position: then you go.

From Emerald

Professor Zéphyrinthe Academy's instructor

« Three dials before you pull the lever: the count, the cooldowns, their position. All green? Then go, and tell your team first. »

Count: five against four
Their top laner is dead: five of you, four of them. First check: the numbers.
Your spells up, theirs down
Their support just spent their engage on nothing; your ultimate is ready. Second check: the cooldowns.
They walk into your zone
They go around the pit and walk into the spot your whole team can reach. Third check: their position.
Go, all together
You engage on three of them, and your team is right behind you. The fight is won before they can answer.
The classic mistake
Four against five: your mid laner is away, your carry is low, their spells are up. You go anyway, no one follows: you die alone.

When to do it

You have the numbers: one of theirs dead or away, five against four.
Their key spell was just used: their engage, their Flash, their ultimate: the window is open.
They walk into your zone: a choke, a narrow bit of river, a spot your whole team can reach.

Check your team first: close enough to follow, and with the health to fight.
Say it before you go: a ping or a word, so your team is ready to follow.
Catch as many as you can: an engage on three is worth more than one on the tank alone.

The classic mistakeEngaging four against five, their spells up, with no one ready to follow. You land it, you die alone, and the fight is lost.

Good to knowNot engaging is a choice too: if the three checks aren't there, wait for a better moment or let the objective go.

Iron to Silver

Before you go in, look behind you: if your team isn't there, don't go.

Gold to Emerald

Count before engaging: who's alive, who's close, whose ultimates are up. Five against four with your team near, you go.

Diamond and above

Engage right after their key spell is spent: bait it, see it go, then go. The best engages punish a mistake of theirs.