Hello Dipen,
You can receive a visitor's visa for any length of period, even more than 1 year but you are not supposed to stay in the UK for more than 6 months at any 1 time.
You also need a letter from your friend confirming where you will be staying and yes, proof that you are financially able to support yourself here (bank statements/payslips).
That's about it, providing you got no criminal record, you are set to go!
Hope this helps,
Vish