A sauce with the right body and texture clings lightly to food. Too thin and it spreads across the whole plate. Too thick and it forms unsightly clumps. A classic test for a sauce is to see if it coats the back of a spoon smoothly and evenly. If the texture is less than perfect, here are some ways to fine-tune your sauce or gravy.
Thicken sauce that is too thin. You can do this by adding starchy substances, purees, yogurt or eggs, among others. Look at the other ingredients of the sauce and of your meal to determine which is right. It's better to err on the side of small doses of the remedy while you're fixing the sauce until it's perfect.
Thin out sauce that is too thick. This can happen from over cooking or skimping a bit on the liquid. This is fairly simple, in that most liquid bases consist a few things: stock/broth, wine, water, cream or juice. Whatever base you were using, add small amounts to it. If you're making a wine reduction with orange pulp in it, dash of orange juice might be a creative fix.
Even those nasty lumps and curdled sauce. This can happen for any number of reasons. Overcooking, too much starch-based or non-liquid substances. When this happens, you usually can add a lump antidote. Trying straining the sauce through a sieve. If you don't want to lose the flavor or quantity, try putting the sauce in a blender. Lastly, you can disguise the curdled sauce with garnishes like nuts, olives, zest, mushrooms are anything that might compliment the sauce without overwhelming it.