Par-boil your potatoes, until starting to go soft and flaky on the outside but still quite firmish in the centre. Drain them, leaveto stand for a bit so the steam comes off them, then put the lid back on the pan and give them a good shake. Don't go OTT (especially if you have boiled them a bit too much) otherwise they will disintegrate and you'll have roast mash. 
After shaking look in the pan - they should be nice and bashed up around the edges; this is what will give you a crispy crunchy coating. Lay them out out a flat try to cool, and dust with seasoned flour. (I use a mix of flour and semolina but it's not a big deal if you don't.)
Once they are cool, put them in the fridge. You can do this the day before.
When you are ready to cook them, heat your fat of choice (for fantastic flavor I always choose either a tin/jar of goose fat or a good old fashioned block of beef dripping. But you can use olive oil (not extra virgin) or lard or sunflower oil - whatever.
It's best if the fat is really hot, so I usually get it to a good heat in a small pan first, then pour it over the potatoes and whack them in a very hot oven. Turnt hem once or twice halfway through. To get them nice and crispy on the outside and fluffy on the inside you need a bit of space around them in the roasting dish, but if you have a small oven and lots of people that is not always possible. No matter, it just means you need to allow longer for them to crisp up. If you can space them well and have the over very high you can do them in half an hour flat, but realistically they usually take longer, what with the stuffing and pigs in blankets etc.
Take your turkey out earlier cover it in foil and leave it somewhere to rest while you do all this. It won't hurt to leave the turkey sitting for an hour or more.
Personally I never put the meat juices around the roast potatoes, as although it gives a great flavour it deters them from going really crispy. I use the meat juices for the gravy though.