Hi,
j think the suggestion of using sdcc is a good idea for a student.
Anyway if you want to continue using Keil j can suggest :
- Use a higher optimisation level.
- Use the small memory model
- Set the "code Rom Size" to "small".
- Enable the "global register coloring" option. This will increase the compile time but usually save some bytes of code.
- If you use pointers try to use memory specific pointers like :
char data* Pchar. This will help a lot but however you loose flexibility.
- Try to use variables of 8 bit lenght maximun (remember 8051 is a 8 bit microcontroller).

However the effect of the solutions depends on your application, and how the code is written.

Best regards.

Massimo.