Sanding is an art form.  It's an integral aspect of real building (not ARF assembly).

Beveling and rounding leading edges is tedious, requires precision, and either yields uniform results or horrible messes.
After building 300 models, I have gotten to the point where I do most of it by hand.

I use a 12" block, 2" wide,  by 3/4" thick.

But, If I have many long pieces of aileron, elevator, stabs and rudders to do (or building multiple airplanes at once and have dozens of edges to work), I'll set up a 45 degree router bit in my drill press and using a guide fence, take a "first pass" cut. This establishes a uniform line to then "work to". From this first bevel, a few swipes with 50 grit gets most everything formed and ready for finish sanding

Perhaps most critical of all is the selection of sand papers. Using too fine of paper early in the "forming" stage allow softer grains to be eroded while stiffer ones remain. However, it is obvious that one extra stroke with a heavy grit can quickly take off too much. Patience at this exact moment renders results you have to live with for the life of the model.

Sanding is a challenge but one of the most important techniques in building. Just have to learn what works, and get really good at it.

Oh... now that I am done here, I am heading back to the shop to shape a leading edge to a wing from a 1/2" x 1-1/4" chunk into an ever changing radius. It'll take me a few minutes... step by step.