What waiter might take for family line-up? (5)
I believe the answer is:
order
'what waiter might' is the definition.
I can't judge whether this defines the answer.
'for family line-up?' is the wordplay.
'for family' becomes 'or' (I am not sure about this - if you are sure you should believe this answer much more).
'line' becomes 'red line' (red line is a kind of line).
'up?' says the letters should be written in reverse (in down clue: letters go upwards).
'red' back-to-front is 'der'.
'or'+'der'='ORDER'
'take' acts as a link.
Can you help me to learn more?
(Other definitions for order that I've seen before include "Symmetry" , "Society of monks/nuns" , "An authoritative command" , "Direction; class; arrange" , "Mr Speaker's plea" .)