The thing that has helped me the most, is I only fire the tater gun by itself. Never with the MGs... Do that for awhile and you will get a better feel for the trajectory when you can easily see the tracer of just the 30mm. The tater has also helped me to remember the absolute importance of unloading the wings before pulling the trigger.
FLy the k4 for awhile and you will get the hang of it, but for me, it has helped me by forcing me to manuever for the shot that I want rather then pulling the trigger and hoping for a lucky impact.
Don't mistake me, I'm not one of the k4 savants of AH... Just a guy who has been flying it off and on for a few months.