In an empty container (I like to use empty wine bottles) pour in a bit of sugar (maybe enough to cover the bottom of the bottle), then add the fresh squeezed lemon juice from 1 large lemon, followed by 1/4 cup of rum and 1 can of lemon-lime soda.
Cap the bottle, and shake. Open the bottle to let some of the built up Co2 to escape, then close and let chill in the fridge.

To drink, get a 6oz glass fill it with ice and pour in the hard lemonade, and save the rest for later.

This is great on a summers day.