The style depend on the look you want. Me I prefer a straight valance, gathered not too much and about 12 to 15 inches deep. I measure the window width and add a third for the gather. By keeping the style simple I can have a variety to change out if I get bored, also it it deep enough to hide shades or blinds if I want the option of darkening the room at some time. I have used quilt weight cottons but I really like the home dec weight fabric. The advantage here is a lot of times you can get it in 54" width which saves on seaming. I see lots of great Home Dec fabs on Fabric.com for about what you pay for regular cotton. I will say don't use silk unless you line it as the sun will rot silk in a very short time. I have also found great old time tablecloths at the thrift shop and they make great valances for a cottage look. In fact I have some up in my sewing room now.