P0300 is unfortunately a generic code which has many different possible causes and solutions. I could list 10 of them, and others could come up with 10 or 20 other ones. But doing that would be pointless unless you are prepared to DIY this work yourself. And some tools (multi-meter, OBD real-time reader, vacuum gauge, etc) may be needed in order to diagnose and find the cause of the misfire. Assuming you don't want to become involved with a potentially complex DIY repair job, I'd recommend finding a good independent shop to diagnose what's going on with your Aveo. That's usually a much better choice than a high priced stealership.