If you just want something quick go for Canon's regular 75-300mm lens without the IS
. It has the same optics in it from everywhere I have read about it.
From seeing your shots of late, I guess the one pointer I can give that will help the most is get the weather/lighting in your favor. Go out on a clear cloudless day. Aim for early mornings or early evenings. That will give you the best time to play around and learn. You will never learn a whole lot when that high cirrus layer is overhead. That is the worst! Also, Try out the approaches to the 16s and the 35s. You will draw the least amt of attention there and get the most traffic there.
Oh yeah, one more tip. Something has to fill the frame. It doesnt have to be an airplane. I have one with my 2.0 MP
C700 with a tiny plane in front of a huge Cb. The plane may be small but that cloud filled the frame. It is going to be nearly impossible getting a shot on without filling the frame with something.