Service tax deduction on website development

Hello,

I am new to this club and new entrepreneur. Our company is pvt. ltd. company and we deal with website development services. My question is : we have taken service tax no. and have applied the same (12.36%) on the amount of website development for a govt. college as they have demanded a necessity of service tax in the invoice. So i just want to know

   1. should we deduct service tax (compulsary) on all further invoices generated by us.

   2. If we are generating invoice dictating advance payment of a project, is the same liable for service tax.

   3. While generating invoice on advance payment shoud we reflect the whole amount.

Thanks in advance.

Please answer as early as possible.