the "big 3" is upgrading the main ground cables from the battery to the chasis, block to batt, and power from the alt to batt. will help with the flow thwoughout the car.
think of it this way. if you roll a marble down a garden hose it will get to the end, but may slowdown throughout the hose due to not having enough room to move properly. now take the same marble and put it down a 3" pvc pipe. it's gonna roll down it in record time and in a more efficient manner since there is more room to move. electricity works the same way. if you have a larger path to move through it can move faster and flow higher amounts through a certain point.
stock is about an 8 guage wire, going to a 4 or even 0 guage will help everything flow more efficiently.
2010 Volvo C70
2011 Harley FLHTK
Midwest Crew #22