A few efficiencies can be found around the IN commands that take signals from the keyboard.
Wherever there is a LD BC,#0000 followed by an IN A,© - this can be replaced with a LD A,#00 [the value that was previously being loaded up to B] followed by an IN A,(#FE).
Also, in places where a routine responds to any keypress from one or more entire half-rows of keys*, you can replace this sequence:
which leaves the Zero flag reset if and only if one of the appropriate keys is pressed, with this:
CPL [Note that the CPL command leaves the Zero Flag unchanged, even if the Accumulator ends up with a value of #00.]
INC A [This replaced the CPL command, which didn't work. INC A will set the Zero flag if and only if the previous value of A was #FF i.e. all bits set, because no keys in the relevant half-row are being pressed.]
which has the same effect on the Zero flag, but requires one less byte.
(*Such as pausing/unpausing the game, toggling the music on/off, or pressing a Jump key other than '0'. It wouldn't work when specific keys out of a half-row are being tested, such as Left-Right movement or the SHIFT+SPACE abandon-the-game key combo. Note that this won't work if the situation requires the precise value in A - as determined by the particular key in the half-row that was pressed - to be used for other purposes.)