Introduce wooden furniture and/or accent pieces in varying tones to break up (but complement) the monotony of the paneled walls. Style can range from 'rustic/weathered' to painted 'french country' to pristine antiques, or any interesting combination thereof.
Country atmosphere is all about 'filling' the space; a basic palette of weighty pieces with primitive and/or delicate touches. Colors and accents are a matter of personal choice, but I prefer hues of earth and sky in rooms with a rural feel. Rusty reds, pale blues, creamy whites, subtle browns, dark greens, etc.
Lighting is crucial; use multiple lamps with warm incandescent bulbs at night, and let in natural light during the day. Keep wall decor simple, but look for unique art and interesting found objects to personalize the space. If the room ventilates well, throw in some houseplants to make it feel happy!
In essence, start big, work small, and don't be afraid to mix it up!