Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.
Beat in the eggs one at a time, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt.
Gradually blend the dry ingredients into the wet mixture until just combined.
Stir in the rolled oats and any optional mix-ins (raisins or chocolate chips).
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them 2 inches apart.
Bake for 10-12 minutes or until the edges are golden brown but the centers are still soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.