Add the simple syrup (1 cup water with 1 cup sugar), lemon juice, sliced strawberries, and 4 cups or more of water. Stir to combine. Taste and adjust flavors, if you want it sweeter or sourer.
Before serving you can add the lemon slices to the pitcher or dispenser or just garnish the cups. I find that when you add the lemon slices and let them sit, it can make the lemonade too bitter.