Rusty galvanised metal sheeting, how to treat and paint

[Mr Chibs]

I've some kind of fascia boards fitted to a shed that previous owner had made, glav sheet with a bend, as the gutter had been leaking for ages, there are rust stains in quite a few places.

I would like to have a blast at painting them, now I've fixed the guttering.

What would be the best way to treat the rust on this surface, prime and then paint them.

TIA

 

[sparkwright]

Special metals primer. And a rust killing primer on the rusty bits.