Tablescapes are sneaky. They always look so complicated, but in fact can be quite simple and effortless. Don't worry about finding the balance between arranged and too arranged. The moment you stop thinking about it is exactly when it will come together.
Remember that balance is more important than perfection. Different elements have their own unique look and feel, but should still compliment other features. When you take a step back from arranging, your eyes are able to focus on the arrangement as a whole.
Another great tip is that less is more. Going overboard on the centerpiece may impede on table space for table settings. Especially for long, narrow tables, stick to the rule of thirds (have the arrangement stay in the middle third of the table). Popular in photography, and applicable in tablescapes!