Always work around a focal point in the room, be it a rug, or a painting, or your most priced possession. One of the most common mistakes people do is hiding their fireplaces, which can be the biggest focal point of the room. Placing the furniture around the fireplace and accessorising it will bring a big difference to the room.
I have seen lot of people who are afraid of colors, fearing it may turn out to be too bright or too dull. My advise is, don't fear the colors. You'll be surprised how beautiful it can turn out to be. Select your favorite color(s). Choose which one of them inspires you most and play with them.
Size and scale of the furniture, paintings and the accessories are the key elements of the design. It should be in accordance to size of the room. Large furniture in a small room makes the room look cluttered and vice versa.
Be it eclectic, modern, contemporary or traditional, always try to mix and match. It doesn't matter if you like something very traditional, you can always throw a couple of modern elements to it.
No one likes to come to a cluttered home. Keeping the place functional and clutter free is integral to interior design. In small spaces, keep things simple, light and airy by using wall or floor shelving units with glass or mirror doors.