What type of prep would be needed to repaint timber stairs?

[DeeM91]

Hey Community,

I wanted to ask please for a little assistance with this DIY job of mine outside. We have recently moved into a new home and previous owner has painted over the natural timber wood stairs outside our garden. Home is less than 12 months old and the paint is already peeling outside from the external conditions. 

I wanted to ask if we were to repaint the same colour, what prep would I need to do before I repaint this staircase?