Find out everything you can about the agency and the people who will receive your pitch. See if you can figure out what companies will be issuing competing proposals or bids. Figure out what your company can provide that others can't. RFPs and IFBs are densely detailed documents. You'll need to read and reread the information carefully to determine exactly what the agency wants.
Close study is especially important for RFPs.
Unlike sealed bidding where price is the government's chief concern, negotiated procurements allow agencies to consider factors other than cost when awarding a contract. Make sure you understand how companies will be graded and what factors will determine the final decision. Make them understand that you can give them what they want at a fair price in a deal that makes them happy. Be ready to accept defeat or prepare your options for fighting the decision. A failed proposal does not condemn a company.