If it is in a bathroom - stay away from moire or fabrics that water spot or are affected by humidity. When you shop for fabric, you can buy it from drapery sample books or from stores that stock fabric. Check your fabric very carefully to determine where flaws are before you cut into it. If you can put the flaw in the back of the heading or hem, go ahead and use it. If it is going to end up right on the face of the drapery, take the fabric back before you cut into it.
Flaws only show up worse when the sunlight is coming through.
Lining is extremely important. Never line draperies with an inferior, cheap lining. You need a good quality lining to protect your fabric from the sun and any condensation around the window. Look for one that is sun resistant and water repellant. Don't skimp here.