Start with the usual cleaning to get rid of any mold release.
Vinyl kits can demand a blood sacrifice when trimming and fitting for the unwary. Softening the vinyl in hot water (remember you are putting your hands in it) or with a hair dryer (some vinyl reacts to hot air and gets brittle) makes it easier to trim, reheating when the vinyl starts to cool and cutting gets harder. Vinyl has a memory so do not let a part cool while bent or it will stay there. Test fit while trimming to make sure there is no deformation.
Parts can be adjusted with heat to alter a pose. Heat the part, carefully bend it into position and run it under cold water to set the position.
Heat can also make your masterpiece sag as it sits on your shelf. Don't display it near a heat source or in a sunlit window. Filling hollow parts with plaster or packing with newspaper can help prevent this.
CA and/or Epoxy glues are the usual adhesives of choice. Heating one part can help reduce gaps as the unheated part can be pressed into the softened part for a tighter fit.
Small seams can be filled with model putties, larger may require epoxy putties.
Most primers will work on vinyl except enamel, it reacts with many types of vinyl and will remain tacky. Some say only use an acrylic based primer. Mr. Surfacer, Tamiya Primer or automotive primer can all work. Test your favourite on some of the flash you have removed from the kit.
With the primer on, the regular arsenal of paints can be used to finish the kit.
Cheers,
Rich