i feel the number 1 best way to get consistent looking lines is to not to tilt the camera upward to much. After a certain amount of practice you'll understand the relationship of how much camera tilt is needed depending on the distance between the glass and the skater. also understanding the basic rule of thirds for filming fisheye on a single obstacle will help your composition on handrails and stairs. i recommend not free handing anything untill you get used to the viewfinder also. a tip when first trying to freehand i used was to take off the viewfinder and use the little lcd to help compose the first frames of the trick and go from there. just go out and film and as long as you watch and learn from your mistakes you'll learn new things everyday.