Many , many articles are in print about sanding, sand papers, etc. But none of them have ever actually said how to sand. Lots of info about grits, wet/dry, sanding blocks, etc. 
I have been watching several of the videos put out by Bob Hunt and Windy Urtnowski. Also I have been thinking back to my time in Idaho and my friend Al Culver. Al used to build models for the Boeing wind tunnel back in the late 50's early 60s, so he knows how to use sand paper.

My problem, I finally realized, is that I was watching these guys sand, but not SEEING!

It finally dawned on me, watching Bob Hunt doing some sanding on various parts in all of those videos. What he and Al do is this: They both sand only in one direction in light strokes.  Click, it made the light go on. I have been sanding, using all the proper grits, sanding blocks, wet or dry, etc. But I was sandng back and forth. This tends to make a high spot in the middle as we can't help but rock our wrists in that type of motion.  The result is a smooth surface, BUT NOT FLAT. It really stands out once the paint is on the plane and looks terrible, shiny or not.

So thats my problem...one of many , im going to start doing that  Thanks for info

A hard flat sanding block is mandatory for blocking out a shape. Never use just paper and your fingers!
Don't try to contour  a compound curve all in one session, you'll be chasing shapes till you've gone too far.
A L/E of a wingtip (solid) is a good example, get the contour of the leading edge then the curvature of the tip. The profile of the tip viewed from the front should be the last item along with final blending.
Multiple steps, inspect your work. Works for me.