Common ground for triggers on 360 controllers?

sorry in advance cuz this has prolly already been handled but where is the common for 360 controller triggers?

If it is a common ground controller (some are not) then by definition, any ground point will work. All ground points are connected on a common ground board.

ok thx so theres like 3 on this standard 360 controller. now im a little new to soldering and pretty much stick building in general but im having trouble soldering a little dollop of solder onto the directional pad because I have such a small area to work with. any advice on technique?