Size: Break up the large expanse of the floor with area rugs.
Pattern: Pattern seems to take up space. Pattern used in large areas - the walls or floor - will make a room seem smaller. Large patterns are best used in large rooms. Large rooms can take more pattern than small rooms. Generally, the more pattern in a room, the greater the sense of coziness.
Colors: Bright or dark colors on the floor will seem to draw the walls in closer.
Textures: Soft, uneven textures are really cozy. Think of deep rugs, or your fur throw. Soft carpets and fabrics convey a sense of warmth, intimacy, and privacy.
Size: If you want to stretch a space, smooth it out. Sameness smoothes. Use a continuous plain wall-to-wall carpet similar in color to the walls. You could also get away with a room-sized rug, but avoid area rugs.
Color: Pale neutral or cool colors. Pale colors reflect light and make the place seem airier. Neutral and cool colors recede, they seem farther away than they actually are.
Plain: In general, avoid patterns. They break up space, and you want to smooth out the space.
Textures: Smooth textures have no surface variety to attract attention; they keep the eye moving on. You will want the floor treatment to be smooth and continuous, wall-to-wall. Make sure the surface is even, not shaggy or carved.
Fiber: You might use polypropylene olefin indoor/outdoor carpeting continuously from outside deck to indoors to link the indoors with the outdoors.
Colors: Repeat indoors the colors you see outdoors. If you see green grass all year long, pick a deep-pile carpet in the same green and then the indoor and the outdoor spaces will seem like one continuous lawn. If you see the sea, bring in the blues and greens.