Put the lemon in lemonade.
If using a fresh lemon: Using the knife, cut your lemon into two large pieces with a single slice down the middle, and put one aside (you will only need 1/2 a lemon). Slit the lemon's flesh several times so the juice will be released easier. Squeeze as much juice as possible out into the drinking glass. Remove seeds, if any.
If using lemon juice: Measure out 2 tablespoons (20mL) of lemon juice and add it to your drinking glass. Vary the amount depending on personal preferences.