How to decorate rectangular living room that has ...

Without seeing the room, its size or your furniture, my suggestion is to start by placing the couch and coffee table in front of the fireplace if this is your focal point and maybe a small table behind the couch.  Place the rest of the furniture in seating groups leaving ample traffic areas thru the space.  Visit some of the decorating sites to find one similar to your room.  This always helps even when you have experience. 

I am not sure if i did understand the question correctly - do you have or have not the fireplace? If you are I think that everything should concentrate on it - you don't have to make anything fancy on the wall or at the floor - just concentrate the focus on the fireplace.

Please specify what was your question about.

Since you don't have a fireplace, it would be good to decide what should be your focal point and work around that to make an appealing seating arrangement -- it could be a large window if you have one along the long wall, or an armoire or cabinet with interesting prints hung on either side.....something to draw your eye when you enter the room.  In a rectangular room it's good to place the sofa across the width of the room instead of along the wall -- this helps widen the room and give it more interest, rather than lining furniture up along the walls.  A sofa table behind it to add accessories helps, too.  You could make an L with a matching loveseat (facing the 'focal' wall) or place two chairs across from and facing the sofa, with the whole arrangement anchored on an 8'x10' area rug.  You can use a chest or buffet type piece along an empty wall, with a lamp and accessories on it and a picture over, taking care to make the whole arrangement 'fit' the scale of that wall.