Well, I generally lay on the primer pretty thickly over 2 or 3 (or perhaps 4) coats of unthinned non-taunting clear. I do this because I hate having to go back and re-shoot area that didn't fill a low spot. A quirk, what can I say.

You need to use a non-loading sandpaper. I like 3M "Sandblaster" paper. The stuff will load a bit but a flick of your fingernail will clear it. I use a block and usually some 220 paper to take it down a bit then switch to 320 to finish out and get rid of the scratches from the 220. Then I usually hit the whole airframe with some 800 to make sure most of the scratches are out. All of this is dry sanding. Then I shoot a coat of very heavily thinned clear (like 80% thinned) over everything to seal the primer though there is usually not much primer lest at this stage. Then I use some 0000 steel wool to make sure all the dust is out of the last coat and I have a smooth surface. Not slick, smooth. Then I start shooting color (as I'm just about to do with my new plane).

Be sure to clean everything really well between coats, especially after handling the thing so much while sanding primer. I use Windex as recommended by Phil "Mr. Concours" Granderson.

Rusty,

I use a tack cloth every time I sand the last coat of primer.  It will not leave any tack behind if you use a light pressure when swiping the cloth.  I use gloves to keep the tack off my fingers and try not to touch the airplane unless I have a clean rag in my hand.  I immediately wash the surface with Windex and then paint.

Paul