According to production fly tier AK Best, "You don't really know how to tie a fly until you've tied a hundred dozen." One secret to making the BWO ride flush in the surface film is to raise the tail just slightly from the plane of the hook shank. Do this by building up a slight thread bump at the tail above the hook barb. It helps to flatten the thread slightly by twirling the bobbin counter-clockwise to undo the natural twist in tying thread (http://globalflyfisher.com/tiebetter/bwos/).  Essentially fly tying is, "the art of attaching feathers, fur, wool, and silk to a tiny hook to create artificial lures that imitate insects, a skill easily mastered by anyone who can peel a grape blindfolded with a pair of tweezers and a butter knife while wearing oven mitts."  "It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman.