If you are presenting, it is best for you to sit across the table from the key members you are presenting to. When you are in meetings and not presenting, it is still important to be visible. If you are in a meeting but not presenting still try to sit across from the high level managers in the room in order to make sure you can make eye contact. In a larger presentation, sitting up in front is best. In this way your presence will be noted and you will be able to focus and interact in an unobstructed way.