You will probably have to compromise between scale spacing and "practical" spacing. All spacings below are center-to-center.
My current layout uses John Armstrong's recommendations from one of his track planning books (which in retrospect were overscale). So I currently have 1 1/4" mainline tangent, 1/3/8" mainline curves, and 1/1/8" yard.
What with all the recent discussion about using closer-to-scale track etc., I am no longer happy with this, and instead should have used the spacings from MR's 1979 N-scale Clinchfield layout (Gordon Odegard), which were 1 1/8" mainline tangent and 1 1/16" yard.
My prototype (1950s SP) used 14' centerline spacing between mainline tangent tracks. In N-scale that is approximately 1 1/16".
If I were to do things over (as I am currently considering doing), taking all the above into consideration, I would use 1 1/8 mainline tangent, 1 1/4 mainline curve, and leave the yard at 1 1/4 as the overscale spacing is less noticeable when viewed from the side. I have tested these spacings with real track and with my worst-case equipment, and they work. This practical testing is important!!!