[Neptunus Rex]

Good rule of thumb for an initial contact is to wait for the bearing rate and direction. Any contact that is left of your heading with a right bearing rate you ASSUME the contact is closing, and at the very least will cross your LOA (Line of Advance). Left bearing rate is opening. When right of own ships heading, left bearing rate is closing and right bearing rate opening.

Always manuever AWAY from the contact until you know (fairly well) what the contacts range is. This also keeps a narrow band contact from being masked by own ship. Same is true of broadband contacts until you know it's range and course.

This is derived by the fact that own ships speed is closing the contact when contact bearing rates are towards your own heading.

Hope this helps. These assumptions on initial contact saved my bacon (and my shipmates) in the real world.