Your Win Condition
Get a solid advantage in lane preferably pre six Poke him to 65% health and then look to all-in and combo
General Strategy
Try to poke him with Q1s and sometimes Q2 in lane Buffer a Q so it goes off while you are slienced
Trading Patterns
Avoid allowing him to get on you for free especially post six. You can E forward or backwards depending on how aggressive he is. Garen’s damage output is very high after he starts getting items. After berserker’s greaves, Garen has a lot of burst and can all-in you when you are about 65% health. He is immobile and has no dashes so you can always look to full combo him.
Wave Management
You want the wave on your side so you can freely poke him without him being able to all-in and look for an extended trade.
Their Win Condition
Survive and outscale Hit spikes and look to take extended trades on E cooldown