Sharps and flats  are always written in the same order in a key signature -i.e.  the first sharp is always F sharp, the second is always C sharp, etc  and the first flat is always B flat the the second E flat etc.  When played at the keyboard, the  sharps fill up from the bottom of the black key groups, starting  with the group of 3 black keys and alternating between the group of 2 and group of 3 black keys.  The flats fill  down  from the top of the black key groups, alternating between the black key groups in the same ways as the sharps.  These keyboard patterns can be seen in the written key signatures: the flats exactly follow the keyboard pattern, the sharps up to the 4th sharp