Place mint leaves, lime juice, sugar and rum to a cocktail shaker. Use a muddler to gently muddle the mint leaves, but don't muddle too much or you'll break up the leaves.
Fill glass ⅔ of the way full with the mixture and ice.
Top with Coca-Cola. Add extra mint leaves and lime for garnish.
Notes
Do not over muddle the mint or you will turn the taste bitter.
Don't overdo it with the mint. A little goes a long way. 5 leaves is enough for 1 drink.
Use sugar instead of simple syrup. It is just easier to use and doesn't require extra steps.
Use dark rum when making the mojito. If you go with white, it won't be a dark color which is the point of this cocktail.
Use crushed ice which will make the mojito colder quicker.