Scale accordingly to how much you feel like imbibing.
1 part whiskey - I tried a few different types - Jameson Irish Whiskey is my favorite so far. You can also experiment with the amount of whiskey - again depending on taste. I've seen recipes up to 2 parts whiskey per 1 part of the other ingredients.
1 part freshly squeezed lemon juice
1 part simple syrup (or slightly less if you prefer it more sour/less sweet) - see below for preparation
You can shake this over ice and serve or just stir and pour over ice if you prefer it "on the rocks". Garnish with a Maraschino cherry and/or a lemon slice.
Add 1 part white sugar to 1 part water in a pot, bring to a boil stirring frequently until the sugar is dissolved. Remove from heat and allow to cool before use. Store covered in refrigerator.