First thing you do is remove the old paint. It comes of very easily with paint stripper. If there is any rust treat it with rust kill.
If you want a factory finish look I highly recommend you remove the fridge door/doors and gaskets/seals and have them sprayed by professionals .
The best option is to have the doors Powder Coated.
But you need to remove the gaskets/seals.
http://www.beckerpowder.com/Powder/BPCWe…
The better option is to have them sprayed by an auto spray painter.
If you plan on spraying the fridge yourself don't use normal white spray paint. It tends to go off in colour, it goes a cleamy colour after a while.
First choice spray paint is a Fridge Paint. Like the one in the site below.
http://www.whiteknightpaints.com.au/prod…
Second choice all pursose White Appliance Spray Paint, again like the one below.
http://www.epinions.com/Paint-Rust-Oleum…
But it all depends where you live as to what choice of brands you have to pick from.
But what ever you do PLEASE DON'T be talked into using normal white spray paint because when it's starts to go off, you wont be happy and you will have waisted all that hard work you put into it.
"I know what I'm talking about, I speak from my own bad experience"