I'm on CN, and I'm not really a lifter, so I've started doing my normal weight x 8 reps x 3 sets, but I've then been repeating another 3 sets, but with half the weight and more reps (15-20). My aim is to get rid of as much glycogen as I can. Will this help gain some strength?, and will it deplete more glycogen than just my heavy weight x 8 x 3??.

I don't see a whole lot of strategy or specifics here...  Let me ask you this:  what is your strength goal?  what do you want to be able to do and what time frame are you trying to accomplish this? what protocol are you using, CNS or CBL?  your weight and estimated bf %? male/ female?Emptying glycogen stores doesn't necessarily constitute a particular gain.  It will obviously help with CNS and fat loss, but your just emptying your gas tank so to speak. To increase strength, you need to progress in various aspects of lifting.