What are the precautions that I should take while filling-up the tax payment challan?
While making payment of tax, apart from other things, one should clearly mention following :

Head of payment, i.e., Corporation Tax/Income-tax (other than companies)
Amount and mode of payment of tax
 Type of payment [i.e., Advance tax/Self assessment tax/Tax on regular assessment/Tax on Dividend/Tax on distributed Income to Unit holders/Surtax]
 Assessment year
The unique identification number called as PAN [Permanent Account Number] allotted by the IT Department.