You've picked out your fabric colors and textures, decided what shape costume you want to make, and now you want to decorate it. As described in detail on the beading page, decorations are made up of lines and shapes. These shapes could be large gems or appliqués sewn onto the costume, or they could be outlined with lines of beading and filled in with sequins. To determine how to fill the space of your costume, you need to choose what shapes or lines will dominate its appearance. The Costume Goddess discusses this in terms of motifs, or shapes. For instance you could have a star motif, or a paisley motif. These would be shapes in the foreground, or positive space, of your costume. The background, or negative space, could be the fabric itself, or could be covered in another color of sequins. Here is an example of positive and negative spaces - the light grey fills the shapes, and the dark grey is the background.
Another alternative could be to have only lines without a center positive space to fill - such as zebra stripes, or the color example above with spiral lines on it. You could have a costume covered in words spelled out in beads. Some things to consider though are the spacing and symmetry of your embellishments. Imagine that each of your spirals is a magnet floating in space. If it gets too close to another magnet they will lock together. So you need to ensure an even amount of space - like an aura - around each of your embellishments. That distance can be zero, as long as it is consistant. Don't have one spiral floating all alone and three right on top of each other.
The Golden Ratio, described above in the Shape section, can also be used for determining the ideal shape, spacing, and relative size of your embelishments. Spirals, flowers, leaves, or anything "organic" will tend to follow the Golden Ratio. And even man-made works of art, such as jewelry,
follow it as well. The Taj Mahal was built with proportions according to the Golden Ratio. Use it, and it will make your design more beautiful.
To be symmetrical or not to be symmetrical - that is the question. It is very pleasing to the eye for a costume to be perfectly symmetrical. Again, even in clothing, it is a subconscious indicator of health. But asymmetry can be very pretty as well. Here are examples of two bras I've made that show symmetry and asymmetry. Coincidentally they also show a dominance of positive space and negative space, respectively.