Recipe:

Ingredients:
* Fresh Mint
* Sugar (preferably darker sugar such as brown or demerara.  It also helps to have a coarse and a fine sugar, so I usually use Sugar In The Raw as well as either brown sugar or natural cane sugar)
* Lime
* Ice
* Rum (a demerara or sugar based rum such as 10 Cane is nice, but not necessary)
* Seltzer/Club Soda

Instructions:
1. Rinse and pluck 10 mint leaves
2. Muddle with 2-3 tsp sugar
   a. Use the coarse sugar if you have both coarse and fine
   b. I use a small wooden mortar and pestle that I like a lot better than my muddler.  I personally want the mint reduced to tiny bits
3. Add the mint/sugar mixture to a roughly 9 oz. tumbler
4. Add juice from 1/2 lime
5. Add 2-3 large ice cubes
6. Pour in 1.5 - 2 oz. rum
7. Add 2-3 tsp fine sugar
8. Stir
9. Top off with seltzer or club soda
10. Stir
11. Enjoy

Experiment and figure out the mix that works best for you.  You will likely need to stir a few times while drinking, as the sugar likes to form a suspension and sink to the bottom.
I like the mojito to be pretty limey.  Sometimes I used a whole lime in Jersey City (the limes there were tiny), but half a lime from the Somerville stores (which are large and very juicy) is plenty.
The amount of sugar in particular has a big effect - use 3-4 tsp total for a fairly bitter mojito, or 6 tsp for a fairly sweet one.