collect advance deposit money / cheque first, goto the main traffic department at E ring Road with prospective buyer, collect the transfer forms and get it typed to transfer the vehicle.

Carry the copy of your ID or passport for your identification and original Mulkiya (vehicle ownership card) to the traffic dept, they will do the rest...it may take around 2-3 hours due to rush.

Collect the full amount prior handing the keys of your car finally to new buyer.

All the best.....which new car you bought?