Mascara, you'll be happy to know that the trick to making a shoelace-type bow hang straight is simple!
Start your bow exactly as you would tie a shoelace: single square knot, then make a single loop with one of the laces. Now, you're about to wrap the second lace over the other to make the second loop and finish the bow -- STOP -- wrap it UNDER instead of over, then push your loop through and tighten the bow, just as you would normally do.
That's the only difference -- wrapping under instead of over. It takes the twist out of the second bow loop where it goes through the main clumpy part of the knot.
This shoelace-related bow is the easiest one I know for use on clothing with I-cord or string ties. It would be fun to take some beautiful decorative ribbon and try some of those fancy floral ones posted by Hildegard, though.