For the modern feel designers recommend using an odd number of pillows in the space. Such as 3 or 5 on a sofa or bed. Shape and size are are just as important for the style you want to create. Keeping with the modern feel you should look for pillows that large enough to see a pattern or geometric shape, for solid colors the larger the pillow the better if will showcase of the pop of color. Using an unexpected shape,such as oblong, will continue the modern.
Selecting the right fabric and color is another way to fully bring the modern look together. Limited color palettes are ideal for a modern, clean line look. Using geometric shapes, and prints on smooth tight woven fabrics, such as cotton and linen, will feel true to the modern home. When choosing your colors look towards art work, accent chair, or rug to pull a color or two out of.
Pillow trim is not normally used for the modern pillow, if you do choose to use it keep the trim color in the same hue as the main pillow color and style, less is more in this department.
A few Modern ideas found on pinterest
Traditional color and styles, on pinterest
Staying true to tradition style try choosing pillows in velvet's and silk. Laying colors, fabrics and textures with prints in floral, plaids and paisleys will make the room feel alive. When using busy pattern such a floral and paisley pair them with pillows in the plaids, solid or strips, using only 2 or 3 of the colors.
This is were pillow trim comes alive. In the traditional style trim is everywhere. From braided edges, to pipping or cording, and tassel on all four corners of a pillow. Try keeping large trim to the large pillows, and using smaller trim in the more delicate pillow edges.