2 things.
First is butter (and any flavourings you want) under the skin.
Second, and most importantly, put your bird on top of some carrots / onions / whatever to raise it off the bottom of your roasting tray and pour cider into the tray. Cover with foil and roast. The cider streams it while it roasts and it's bloody awesome. Remove the foil for the last 30 mins to crisp it up.
I guess you could use other liquid. But use cider.