I like ginger (crushed up finely) and a whole lemon squeezed, and sugar and water. That's it!
The first few times, I simmered quite a bit of ginger (like almost a whole root, peeled and cut into pieces) and then added the sugar. That was really good, but I wanted more of a ginger bite this time so I just grated and crushed up some fresh peeled ginger. I just added that to the water and sugar mixture and shook well. I didn't want it in the final product, so I waited a couple of days and then strained it into a new container. Then I added the carbonator cap (but if you were using yeast, that would be the time to add the yeast). I used a 2 liter bottle, so it worked great for me.
Here's the basic procedure I followed: Homemade Ginger Ale