I smear mustard all over teh top, crush some garlic, chuck on a sprinkle of flour, break up a few OXO cubes on top, then put a knob of butter on the top.
I also put about 1/2cup of water in the bottom of the dish which stops the roast drying out.
After about 1 hr or so, I put in the spuds to roast. About 45mins to go, take off the lid and let it brown, and dont forget to rest the meat. Ideally meat should rest for as long as its cooked, but I find that a roast is OK with resting for about 20-30mins or so.