The cabinets (doors and styles) will need a good sanding to remove any loose paint. Try to feather out areas where the paint is well stuck. The sanding will also help take care of thick areas or runs.
Now wipe everything down with a damp rag to remove the remaining dust. Using a liquid sander/deglosser like Paso will also help as it chemically etches and cleans the surface.
After the sanding and cleaning a primer and paint can be applied.