use the pan the meat has roasted in
deglaze with a splash of something...brandy, wine, cider, veg stock
get all the gubbins off the pan with a wooden spoon
then I will swish round the roasting pan with the potato water/other veg water and get it all into a sauce pan, it somehow seems easier to deal with in a proper saucepan
plenty of S&P, an appropriate OXO or two, a spoonful of something sticky I often add in some odd bits of stuff...mango chutney/cranberry/chutney...not all, just pick one!
If it's still not right try a dash of Lea and Perrins, maybe a teaspoon of balsamic or a spritz of lemon
I generally thicken with cornflour slurry....or if you are making yorkshire puds a swish of the gravy round the batter jug and back onto the heat will usually work.
Most gravy failure are down to a lack of salt imo....salt is gooooooooood and tasty.