The key to a good gravy are good pan juices. Now I assume you perhaps want to make a gravy to accompany a roast?
I will walk you through how I make a very simply (yet delicious) gravy when I cook a roast chicken.
1) Roast your chicken (and vegetables, if you want) as normal. I like to place my chicken on a rack to keep it off the bottom of the roasting pan. I cut off the wings of the chicken (and maybe add another 1 or 2 wings that I have bought seperately) and place them on the bottom of the roasting tray. This helps produce more pan juices as well as enriching the juice's flavour. Roasting any vegetables in the same tray will help the flavour as well (particularly carrots, onions, garlic, pumpkin and any herbs used).
2. Remove your chicken and vegetables, cover and keep hot. Scrape the roasting tray with a wooden spoon to get all the tasty bits and pour all of the pan juices into a jug and add a handful of icecubes to help seperate and congeal the fat from the juices.
3. Place the roasting tray you used (assuming its metal) on the stove. Add a couple of spoonfuls of the chicken fat back to the pan (or you can use butter or oil). Add a spoonful or 2 of plain flour to the tray and allow to cook gently for a few minutes to cook off the floury taste and allow to take on a little colour (a 'blonde' coloured mixture is what we are aiming for, or for those up on the speak, a blonde roux).
4. Add your reserved pan juices to the fat and flour mixture. Use a whisk or something else suitable to get rid of any lumps and combine the mixture well. Allow to cook gently until the thickening action of the flour has set in. If it's still too thin, add a touch more flour and let it cook for a bit to see how much it thickens up. Repeat if necessary. If you go a little overboard with the flour you can always add more water/chicken stock/white wine to thin it out a bit.
5. Taste the gravy and season if necessary with salt and pepper. Some finely chopped fesh thyme also goes really well. Serve it up.
That is how I prepare a simple gravy from pan juices. It is pretty much the standard technique no matter what direction you take it in. Hope it helps.