For the head, I recommend non-ionic shower cleaner. If it's dusty, use the pointy thing from the vacuum cleaner. For varnished wooden bits, use Pledge or Mr Sheen. For unvarnished wooden bits (eg fingerboard), use lemon oil. For metal bits, leave alone unless green deposits are forming, at which point get some of that expensive Amway metal cleaner. Remember, the banjo will be more pleasant and easier to clean if you cut those four or five unsightly wires off the front and throw them away.