Black marks? Are they from rubbing something? If so, I'd say try to polish them out first before you try and paint anything.
As for the chips, you're better of using a touch up brush to fill those in. if you're really detailed, you can fill them up a few times (to make them level with the paint), then use an electric polisher to buff it out even (make sure not to burn the paint if it's not an orbital polisher).