Bike hard, all the time.

I've been riding fixed for probably 6-8 Months now, before that I had a period where I rode my road bike really heavily for 4-6 Months (~60 miles a week, commuting everyday) and I just rode hard, oddly enough in interval. I'd mash up a hill, if I couldn't mash, I'd down shift and push as hard as I could. I'd recover on the down hill and start pushing super hard (glendale going into echo park) and merge into traffic at speed.

Now on my fixie I do the same thing, mash a hill, recover on the down hill as much as I can and burst out of the down hill spinning like a mad man. Climbing, downhills, ups and downs, long straights. I regularly go from the absolute rear to the front in group rides, fall back, do it again.

I rarely just "pedal"

My point, if it isn't clear, is do interval training and consistently push yourself to find results. Also consider gearing down. I know glendale is flat but I find spinning faster easier vs mashing harder in terms of distances. I'd say try something in the mid to low 70s in GI.