Go ahead and clear the table, and clean it. Now get and take the longest table cloth which you have and place it in the center of the table. This cloth should be the darkest in color, since it will be the focal point.
However, if you want to dress down the table, as opposed to dressing it up, you can use linen fabrics or plaids in the center. Use a single color, since it will act as a base and won't make the table look crowded.
Now take the half length table cloths and layer them over the first layer of the table cloth which you put down. You are going to want to use a pattern and color which contrasts with the one which you used initially.
Just remember that using a shiny fabric will make the table look dressed up, while anything else will help it dress down.
Now you can go ahead and place a square shaped table topper in the center of the table. In doing so, you will be adding a third layer to your table. Make sure that this is made of light weight fabric and is solid in color.
Place the dishes where everyone will be sitting on the table. Place the glasses top down. You will also be required to roll up napkins and put rings on them. Try getting napkins which match the layers that you have been placing.
Now for your center piece, you should get something which matches the colors of the layers which you have placed. The colors need to be fairly similar and need to match. However, if you have a chandelier, try using a low center piece as opposed to a tall one.