A rotation is a move out of your lane to help somewhere else. The best time to move is when you can arrive before the play is decided and your team can afford what you leave behind. Start with three checks: your wave, the minimap and which teammates can move with you.
Clear the wave before you leave
If enemy minions are about to reach your tower, clear them first unless your team needs immediate help nearby. If you've pushed your own wave into the enemy tower, use that time to help mid, cover your jungler or check the river with a teammate. When the fight ends before you arrive, turn back instead of chasing it into the enemy jungle.
Decide whether to contest or trade
Before walking into the river, look for your jungler, count the teammates close enough to join, and check which opponents are missing. Ping early so teammates can finish their waves and move together. If your team is low on health or spread across the map, give up the contest and look for something safe: defend a tower, clear an exposed wave or pressure the opposite lane if you know where the enemy is.
For example, if you're in clash lane and your team is outnumbered at a far-side objective, crossing the map late can cost both the fight and your tower. Catch the wave first. If the enemy stays visible and the lane is safe, push it and then reset before they disappear from the map.
Take one useful thing after a fight
A won fight gives you a short window. If a friendly wave is already at a tower, push with it. If your team is near an objective and healthy enough to finish it, ping it and commit together. If neither play is available, clear the nearest wave and recall. A clean reset gives you time to recover and spend your gold before the next fight.
Review one decision after each match
Pick the first rotation that cost you a wave, a tower or a fight. Ask whether you left too early, took an unsafe route or kept moving after your team backed off. In your next match, work on that one decision. Check the in-game map and timers each match so your plan fits the game you're playing.