Re-calibrating your CVT can be one of the best bang for the buck modifications. Start by changing the variator roller weights first.
Heavier roller weights =A higher top speed, and a slower acceleration and take off speed
Lighter roller weights =A lower top speed, and a faster acceleration and take off speed
Lighter roller weights will increase overall engine RPM. Heavier roller weights decrease engine RPM. Roller weights can be found for the 50cc GY6 in the range of probably 4 - 12 grams or so. Somewhere around 6 - 9 grams would probably be a good place to start to experiment. Lighter scooters may want to have a little heavier roller weights. Weigh your stock weights using a precision scale and select new rollers weights either lighter or heavier - depending how you want to change your engine RPM range.
In addition to the front driver pulley, the rear driver pulley can also be re-calibrated with different clutch shoe springs to vary clutch engagement RPM, and also the main driven compression spring can be changed to a stiffer spring which also effectively boosts engine RPM under driving conditions. There is a lot to be said about CVT tuning, but to simplify many people can probably benefit from slightly lighter roller weights in the front driver pulley and also a stiffer torque (compression spring) in the rear driven pulley. These changes will effectively slow down the up-shift of the CVT and allow the engine to rev up higher and have better torque under driving conditions. Don't go too far though. Too high an RPM and you might be way out of your power band. Also, too high of an RPM can be annoying while cruising with low engine loads. It can feel like driving your 5-speed car in 3rd gear on the freeway, while costing you gas mileage.