Use bushes to your advantage. Let the enemy pass you up and when you're behind them, then you strike. Charge out with Decisive Strike then once they have been hit, tare them up with judgment. If the health bar is 2 or lower hit them with Demacian justice.

How to use abilities:
-Decisive strike: This is used as your first strike, a way to catch up to an enemy, or to get away.
-Courage: Turn on at any time you start taking damage which will happen if decisive strike doesn't take you far enough to hit the enemy and/ or when judgment finishes and their health is still pretty far up.
-Judgment: As your main damage tool use it as often as possible. Best time to use it is after decisive strike so the enemy cant hit you back. It is also great for farming minions and team fights. SPIN TO WIN!!!
-Demacian justice: ONLY USE IF THE ENEMY HAS 3 OR LESS BARS! In early game i would even wait for 2 bars of health to use it.

This build will give you the tankyness that will keep you in the lane longer and make you hard to kill. As the game progresses this slight health advantage will evolve into an unstoppable tank. The boots of mobility is to get you in battle faster from base and to really get the jump on enemies with decisive strike. After you get the sunfire cape (which wont take long to get) the build begins to focus on building up that damage that will turn you into an AD carry.

Although Garen is a great solo top, I find that it is best to lane with a team mate.