Not sure what to use if it's really rust but if it's dirt you could try a contact spray cleaner. WD-40 makes a electrical component contact spray cleaner that can be found in Amazon . You can also get it from Radio Shack.
if you are referring to your charging port 30 or 9 pin I would find out first of all why you have rust if that is what it is and where did it come from - Did it get wet? if it is even rust you can still use the cleaner iEd mentions or did a Q-tip in alcohol and squeeze all excess out of it and gently wipe it off. Good luck.