Practice, practice, practice. We've all had bad ones some time or other.
A very smooth pan technique is needed, following the airplane from well before the point where you want to take the photo, and to continuing the pan - follow through - even after you've pressed the shutter button, and at least until you can see the subject in the viewfinder again after the mirror has flipped right down.
Then just practice, practice, practice. Try shooting a few pictures with a slightly wider setting on the zoom lens first (assuming you use a zoon), to give yourself slightly more chance to get the whole airplane in the frame. Then, as you gain experience, you can zoom in somewhat closer so the nose and tail come really close to the edges of the frame.
Oh, and watch the horizon, especially if you are taking touchdown and rotation shots - the natural tendency is to follow the airplane and keep it level in the viewfinder, but then the horizon comes out on a slope.