Consider table shape
The shape of your table will dictate where you place decorative objects on it . Circular tables have less options and cry out for central placements as you can see in the photos below . Use variety in shapes and more than one object to create greater interest. The objects you choose to display should also work well with the overall theme/style of the room.
With a circular table the trick is to use scale and variety to energize the display. The two urns are simple and elegant and their height is counter balanced by the visual weight of the circular bowl . Everything blends but it is still interesting because of the objects used.
You can never go astray by choosing calla lilies for a table. They are tall and elegant and the white goes with any decor. They look particularly pleasing in this room where their height directs the eye to the stairs and the shape of the vase seems to nestle into the curve of the stairs in the background.
You have more options with a rectangular table.
You can stretch out your arrangement along the table . This works because of the harmony created by the use of similar materials and interesting shapes. It's symmetrical without being boring.
Using multiples on long tables moves the eye along the length, creates unity and helps balance scale. The crystal vases add an additional texture that works with the lavishness of the room.
Candlesticks
When you use multiples it is bet to keep at least one aspect the same and then use variety. In the shot about you have varying heights and shapes but they are all clear and the same colour candle is used. Less colour always produces a more sophisticated look. . You don't have to have this many but rectangular or circular massing of at least five works best.
Height works when you have clear candlestick groupings. Multiples can create a cluttered look if the variables are not controlled. These holders are so delicate it looks like the candles are hovering above the table. Keeping the candles to one hue and varying it is always an interesting statement.
Crate and Barrel via Live the fancy life
Metal and glass always look good together because of their sparkle especially when candles are lit.
Using a piece of mirror as a runner and placing candles on it is an inexpensive treatment that always look exceptional. You don't have to worry about safety and any melted wax scrapes off with a blade. One
Fresh flowers
You can never go wrong with fresh flowers but you can move your WOW factor from OK to fantastic by considering the container you use and kind and amount of flowers. I love tall flowers on a dining table but you have to consider the space between your light and the top of the floral arrangement.
The use of tall thin vases and a sparse arrangement of flowers works in this room. This is a trick I often use because it cuts down on the the number of flowers you have to buy.
Here's another variation on the theme above. The flowers you choose can come from your own garden too. I manage to always have something fresh at my summer house without a price tag attached to it.
This classic arrangement of fresh flowers in a simple vase and candlesticks always works. When you have candles it is important to keep them straight. Masses of them make any that are not perfect stand out.
Sculptural elements
Go for the unexpected as a table decoration. This arrangement is as interesting as the rest of the space it is part of.
Being an avid beachcomber I would have no difficulty finding interesting driftwood arrangements. This one mimics the lines of the artwork behind it. Simple but very effective.
Some tables are so sculptural they need nothing more added.