Be careful (4,4)
'be careful' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for look out that I've seen before include "A view of the future" , "as Wenceslas did" , "Be on your guard!" , "Take care" , "Beware!" .)
(Other definitions for play safe that I've seen before include "Avoid risk" , "Act cautiously" , "Body of church" , "Don't take risks - its only a game?" , "Avoid taking risks - in game?" .)