Any dimensions that must be maintained after assembly (component to be flush to panel, max. or min. clearance between components or component & panel, etc.).
If coatings are to be applied, indicate area to be coated & state min. or max. thickness (if applicable). It also may be favorable to indicate where coatings are NOT allowed (open frame relays, edge contacts, unsealed switches, slots/holes)
Any secondary operations should be clearly explained (applying tape or adhesive, lead or component forming, relay venting)
Max. lead trim height or component height if it is a concern.
Special handling requirements (anti-static, shock, vibration).
Special testing requirements (usually a separate document referred to by a note on the assy. drawing).
Cleaning requirements (if needed).
In short, any note that will clarify your requirements to the people assembling your product.
