A good Gin Rickey is nothing more than lime juice, dry gin, and your bubbly water of choice, be it club soda, seltzer, or Wonka's Fizzy Lifting Drink (Warning: Consuming a Gin Rickey made with Wonka's Fizzy Lifting Drink may be hazardous to your health and/or altitude. Consumer discretion is advised). Some people may say that you need to add sugar to it, but they are horrible liars that you should shun at all costs. Here's the technique I use...
Squeeze the juice of 1/2 a lime into a tall Collins glass full of ice. Add 2 oz of London dry gin, chuck in the lime shell, and fill to the top with your fizzy liquid of choice. I've been known to add a drop or three of orange bitters as well, but I'm eccentric that way. I've even tried it once with a sparkling blood orange soda, which was really quite good, although I renamed that particular concoction...yeah, since it was orange I decided it wasn't a "Gin Rickey" so much as a "Lucy Ricardo." Please, hold your applause, just throw cash.
It's not a really fancy drink to look at, but it's a damned good drink to have while, say, waiting for those burgers/chicken breasts/brats/steaks/salmon filets/black bean patties on the grill to finish up on your next summer cookout.
Just make sure you don't drink only Gin Rickeys while out in the noon-day sun, even if you are an Englishman and/or mad dog. Stay properly hydrated! Remember, if it starts to look like this... put down the glass and go have some water.