It depends.

If you are dining, then place it on the far side of your plate. If you are sitting at a table, but not dining, then place it approximately halfway between the dining position and the table edge. If you are standing by the table, then I’d go with about 4"-6" from the table edge. If you are standing by the table in a high traffic area, then I’d go with 6"-8". If you notice someone nearby who is particularly animated when speaking, then I’d aim for the centre of the table.

This answer assumes the table in question is a dining table. Coffee tables are a whole different kettle of fish; and don’t even get me started on side tables, bureaus and credenzas!