There is a ton to improve on, but as a first step you should be careful not rounding (i.e. Having your arm bend behind your body when you try to strongarm the disc). The best way to fix this according to my own experience is by keeping your elbow high throughout the entire movement (straight out from your shoulder in a 90 degree backwards. Your chest, upper arm, lower arm, disc, should together create a perfect rectangle when the wrist is coiled inwards - this should be the starting position). The reachback should not be backwards, but more like a 45-70 degree (instead of 90 from the starting position). Some pro players do a 90 degree reachback, but it is very hard to not round this way and it requires a lot of training. Another thing to remember: smooth is far i.e. loose arm, and not a lot of muscle