Artificial flowers are perfectly acceptable, and have the advantage of being reusable. But don't think that a centerpiece has to be floral. Use your imagination. If you use candles, keep them lit until the last dinner guest has left the table. Candles should be placed next to the centerpiece.
Formal dinners seem to demand the use of silver.
Nothing else looks quite the same as polished silver. Avoid mixing expensive china pieces with inexpensive ones. It is traditional for each person, or couple to have their own set of salt and pepper shakers. Allow enough space between each guest to make serving easy, and allow for good movement of people's arms. Place dishes symmetrically, and equal distances from each other.