When attacking an enemy be sure to hit them with Decisive Strike. This will prevent them from using their abilities for a short duration. Then launch Judgment and finish with ult only if your enemy has very low health. Ghost and Courage will help you escape from the range of your enemy's turret without receiving much damage. Tis tactic helps Garen secure many kills with turrets not bing much of a threat.

When facing a combination of strong AD and AP opponents try building items from both categories, with health and health regeneration being your main focus.