Vision & Map Control
Brushes, scouting and fog control
Fog and Vision Basics
The map is covered by the fog of war, so you can only see the area within sight of your allies, towers, and minions. Everything else is dark, and when an enemy suddenly disappears from view, it's very likely they're hiding in a bush or in the fog.
The Tyrant and the Overlord spawn on the river at 4 minutes, so whether or not you can secure vision of the bushes around them directly determines who holds the initiative in the match.
Bushes Give One-Way Vision
Once you're inside a bush you become invisible to those outside, but your position is revealed the moment you attack or use a skill.
That's why you must never face-check by diving in without confirming what's inside. Always scout the bush first, then enter.
Five Ways to Scout Safely
The core of scouting is to reveal the enemy while staying in a safe position. Fire a normal skill in from outside and watch for a reaction; probe the interior with a targeted or recon skill; flush out hidden enemies with a sonic or echo-type skill; sense their presence with a skill that gives audio feedback; and if you're the roamer, use gear or skills with area scouting to reveal lurking enemies all at once.
In every case the idea is the same: don't step into dangerous range yourself, and take the enemy's position first.
If You Have No Vision, Back Off
Always watch the minimap. Once you clear a wave and your minions are gone, your vision closes and the fog spreads. If you get greedy and push into the tower without vision, you'll get ganked.
If you can't see, retreat immediately. Controlling the fog and the bushes, and staying hidden to keep yourself safe, is the foundation of the vision game.