Padding is when you give time before you start your video. For example you say rolling press the button the after 3 seconds you say action so you catch the footage and won't get cut off. After you finish your video you can say cut. You have to do this so you audio won't get cut off and to make your chances better of getting it good.
The weakness of the video is if your audio is cut and you are out of order. The strength is if you get your audio is good and it din't get cut off. You can improve it by going over your video and checking for mistakes and audio check. IMovie is hard to edit if you don't know how to work iMovie and you don't know how to edit your video.