Here is an easy to follow and great recipe that is pretty standard for the New York City bars I've worked in. Feel free to play around with the ingredients to get it exactly the way you like it! There is no wrong amount of bitters, sugar or whiskey. If you want a little sweeter, add more sugar. If you want a little drier, use less sugar or up the whiskey (I prefer up the whiskey...;)) And remember if you're using a higher proof whiskey, you might have to adjust the sugar a little bit because the higher alcohol content will make for a drier cocktail. When I say "a little" I mean about a bar spoon more or less of sugar. A little goes a long way!
Have fun with it and try different whiskeys and bitters too, it's really cool how different a simple cocktail like this can be if you just tweak it a little.
Skål! (Cheers in Swedish)