You aren't always able to have a natural focal point in a room. You know, a fireplace, a bay window, a built in entertainment center...that sort of thing. But a room really needs one to make it feel welcoming, inviting, and restful.
When you don't have the architectural feature, make you own, with a dramatic large piece of furniture, a piece of artwork, an arrangement of plants, a contrasting, painted wall, or perhaps a gorgeous area rug with a conversation grouping framing it.
Whatever you choose as your focal point, it should be the first thing people notice upon entering the room. Whether you have one great masterpiece or a large arrangement of wall hangings and pictures, make sure that furniture is place so that it can be observed at leisure. Lighting should be directed at it, either from track or spot lights on the ceiling.
Perhaps you have an antique table and a rare collection of china. This will make a lovely focal point, if it is readily visible and well lighted. If it is texturally unusual, colorful, rare, or visually appealing, it can be your focal point.
A curio cabinet full of collectors pieces can be lighted from within or with spots. If It is a dark cabinet it should be placed on a light wall...light woods or pale lacquered woods would show much better on a dramatically darkened accent wall.
If your focal point is a large window with a beautiful view, make sure that your furniture is placed in such a way that guests can enjoy it. Add outside ambiant lighting to create drama when it sun goes down.