Intestines really depend. Screamer Pink shaded with Carroburg Crimson gets you fine results, but just painting it brown or purple and then coating with Blood For The Blood God works great too. For the skin, take Duncan's tutorial on Blightkings.
If you like mine: Ogryn Camo in thin layers until it makes an even layer, shade Reikland, dry-brush Pallid Wych Flesh (dry-brushing this paint gives a really chalky finish, if you don't like that, layer it instead). Once dried, make a wash out of 50/50 Carroburg Crimson/Lhamean Medium and wash all the spots you think should look sore, like around the wounds and boils and where the armour meets the naked skin.