I use it purely as a boost so I put it at the very end of the chain. I also use it in either 9v or around 12v. I didn't care for it at 18v. It seemed to lose a good bit of warmth and seemed sterile sounding. Just my preference.
Depending on your amp and cab, the EP may kind of crush your tone, if placed before gain stuff. Therefore I use it after dirt boxes but before time-based effects such as reverb, delay etc...
It set it at unity and never get it off, except if it's too loud.
Gets sone kind of compression as well. Have to like it. Or not.