Paint the walls at either end of the long, narrow kitchen in a darker shade than the long walls. Choosing a shade that is slightly darker places emphasis on the longer walls, thus making the kitchen appear wider.
Hang a mirror on one of the long walls. If you have a large wall space on one side, hang a horizontally shaped mirror. This makes the kitchen appear wider and creates the illusion of a spacious area. Mounting it opposite the kitchen window seems to double the view.
Mount decor on the wall spaces instead of keeping kitchen gadgets and knickknacks on the countertop. Decorative wood, plastic or wire shelves are a wise way to do this.
Install decorative hooks to hold potholders, oven mitts and dishtowels. This adds color and texture to the room without making it appear untidy.
Pick solid colors for the curtains and rugs in the long, narrow kitchen. Another wise option is to use small prints. Bold, large patterns tend to minimize the space.