Based on my (humble) opinion, the first step is to break up the entire space into sections and create the feeling of a series of functional zones that link to each other cohesively. For instance, designate an area in the living room for TV watching and another as a casual work corner, linking to a third zone - complete with settees and all - for spending some quiet moments with guests who pop over. Put on your thinking cap and put up screens or partitions to break the space up where suitable.
Next, consider setting up several points of interest in the room. The TV is obviously one. Other focal spots could be a display unit on the other side, or simply something like an oversized lamp shade. If not, an artwork or a mirror on the wall will also do the trick. Meanwhile, I can't stress enough how handy area rugs will come in, especially in a house where floor area is ample.
Yet, while you are doing all these, remember not to lose your insanity and congest the space with too many furniture pieces too. Leaving some empty spaces in a room is still necessary, and its importance cannot be ignored.
Tags: design, decor, interior design, furnishings