To minimize rust, sand the area down to bare metal, apply a good primer, then the touch-up paint. Follow with clear coat and wax the area to make it look like nothing happened. There is also a rust inhibitor you can put under the primer if you want to be anal, but it really does nothing unless you already have rust.
Maybe I missed a step or whatever, but I'm sure someone will correct me if so.
You can take a pencil with an unused eraser and glue a piece of sandpaper on the top of the eraser. That helps take care of the little details without damaging adjacent unharmed areas. Worked for me on a spot on my roof.
Not sure I know of a good primer to suggest... I tend to do things halfway, so once I get it cleaned up I just put touchup paint over it. :whistling: Doesn't exactly make for an unnoticeable (or long lasting) repair! :innocent: