How much deductions should be done from ones salary?

Dear all,

Suppose a person's gross salary is Rs.8000/-. Now he has taken loan, advance etc..Now to recover this I have to deduct some amount from his salary towards loan and advance, also PF,ESI, PT has to be deducted and also he has to be paid some salary for the month worked. So my question is...

a) How much to deduct because after deduction very less is left over as his take home salary?

b) Is there a minimum level after which one cannot deduct?

   Again not to forget that I cannot deduct the whole salary.

Please help.