Cushions are often used to tie in the color scheme in a room, drawing on the colors of the drapes, accessories, or rugs. You can also make a room look more casual and comfortable by lightly "tossing" the cushions. 

Start with two large pillows at each end of your couch, these can be solid or a print pattern. These pillows will set the stage for your entire look. Once you have these pillows in place you can add interest and charm by adding two smaller pillows in a coordinating pattern or color. This is your chance to really  make a statement. If you feel bold you can also use 2 pillows that match for a more formal look, or two that do not match for a more casual look. 

Adding a variety of textures in your home is the newest trend. To achieve a nice look texture mixing using fabrics in fur, canvas, wood grain, sand, ribbed, or smooth such as glass or marble are a few examples.

Also, don't just add the cushions to your couch, make sure you bring your personal touches to chairs or benches in your space as well.