I use several methods, one is aligning the halves and glueing them in sections so I can bend and shape the seam to limit the amount of sanding needed. I use Tamiya xtra thin so when the two halves are pressed together some plastic oozes out the seam facilitating seam cleanup. Sometimes I will sand the seam flat, other times I will apply some filler and then sand. This works well on models with recessed seams. However the Revell A-10 im currently working on has raised details and panels so Im finding it hard to smooth without ruining the details.
If you are using thin CA, it is important to get the edge of the fuselage halves perpendicular, so they do not meet in a V, but actually come together perfectly. If the sides do not have locating pins, you can put down a full sheet of sandpaper on a flat surface and rub the sides each around on that. If the sides do have locating pins, you can sand the side that has holes, rather than pins, and use fine needle files on the areas between pins, carefully so that you take off a minimal amount of plastic. Remember, thin CA does not fill gaps.
ROFL… resurrected a two year old thread…