Well, then as first step you should be familiar and learn the inside of 8051 by reading a good text book and also the valuable documents which Erik has recommended. Tutorials on this website are also of great help.

I would recommend you to learn assembly language first. You should get a development board and practice the use of 8051 on chip peripherals, one by one. First try to understand the timers, try to use them in your code. Then jump to interrupts and finally to serial port.

If you feel difficulty at any stage, you can post your questions here. Don't ask us for ready made codes, but show us that you have done something and got stuck up. Many of the people here would be happy to help you.

Good Luck