When making roasties, the most important thing is to par-boil them (after peeling and chopping) for 5 minutes, drain, then give them a really good shake in the pan to rough them up. All the scruffy edges are the bits that catch the oil and turn crispy, so it really is the best way to get crispy roasties.
I just cook mine in olive oil- no goose fat or dripping. I don't think it's necessary. Just make sure the oil is hot when you put the potatoes on the oven tray (heat 2 tbsp olive oil on the tray whilst the potatoes are boiling). Sprinkle with sea salt and pepper, some chopped fresh rosemary, add two whole garlic cloves and put in the oven for 45 minutes, turning halfway through. I could eat them everyday!