Well start by figuring out where the throttle is sticking.
Can you manually push the throttle back to idle position? (IE is the actually throttle barrel sticking)
If so, dirt probably go into the throttle barrel. Loosen throttle and spray some WD-40 on your handlebar.
If it is sticking someplace else, I would start buy purchasing a new cable, they are usually in the range of $15. Before you do that, visually inspect the cable from top to the carb, make sure it is routed correctly, no binding etc.
If none of this helps, its probably sticking inside the carburator.
Diagnose where it is sticking and go from there.