I typically shy away from doing this with my Orks- though most of them are Gorkamorka era Brian Nelson models, not the older models. I do have a RT era Bad Moon boss to paint, though, so I've been looking into it more for that particular model. I would start with the midtone for the flesh, and add a spot of Dwarf flesh as highlighting progressed- then continue up through adding the highlight color you plan on using (I usually use GW Rotting Flesh/VGC Dead Flesh). If this color continues on to something that's too green or grey for your liking, you could always use a thin glaze of red or magenta to get the tone desired.
A lot of folks paint Orks with solid red eyes, too... I've never been a fan, as it makes them look too much like monsters. I want my greenskins to have character and a little bit of "humanity" so I paint their eyes like I would other humanoids' (white with a pupil). This way you can really expand on the expressions a lot of these models have built into the sculpts (Cross eyed for Madboyz, etc).