My preferred method:

A sealer like dope Sanding Sealer or Minwax Wood Hardener

(sand smooth)

Wait. Wait longer. Let that stuff outgas.

Elmer's filler, several coats, sanding in between.

Wait a bit. Let that water evaporate.

Prime, sand, prime, sand until it is smooooooth. If necessary, use thick gray enamel to fill cracks and dings.

Wait.

Several coats of paint. Wet sand out any problems.

Dry thoroughly.

Wet sand if necessary. Rub out any haze or imperfections with polishing compound.

Future.

Decals.

More Future.

Buff.