Every time the user changes the selected object (or current
document, last undoable operation, etc.), change the menu
items that operate on it to include the specifics of
the action. Obviously, if there is no selected
object, you should disable the menu item, thus
reinforcing the connection between the item and its object.
Incidentally, this pattern could also work for button labels,
links, or anything else that is a "verb" in the context of the UI.
What if there are multiple selected objects? There's not a whole
lot of guidance out there -- in existing software, this pattern
mostly applies to documents and undo operations -- but you could
write in a plural, like "Delete Selected Objects."