The key issue of negotiation are :
1) First we have to decided the back to wall price.
2) before going to negotiation you should plan all thing by 
keeping all documentation like price list,discount 
structure ect.
3) when we negotiate we do not negotiate on price we 
negotiate on every thing like credit period, payment 
terms,ect.
4) The price should be memorise it means that what is the 
basic price and after giving cash advance discount what 
will be the cost and after giving quantity discount what 
will be the cost.

Still you find difficult then try to take some time from 
them.

the key issues in negotiating are

1.price comparison
2.discounts or offers
3.credit terms
4.company's brand i.e good will of the company
5.updated techniques(any product)