How can I improve this PCB schema for L293D H-brigde?
The main thing is the lack of bulk  capacitance for the H-bridge (the V2 connection) that is tight to GND. LOW inductance, lots of copper.

You need to bulk up on the copper for the GND plane going through the middle of the chip

The 4 traces going to the machine terminals need to be bulked up. 

Your silkscreen placement is non-intuitive to the terminal meaning.