First, find an agent who represents you and not the seller. This is beneficial during the negotiation process. If you are working with a buyer's agent, he or she is required not to tell the seller of your top choice. In addition, he or she is also focused on getting you the lowest asking price.
Also, when you use a buyer's agent, you will see more properties. Not only are they plugged into their Multiple Listing Service, but also they are actively finding homes that are listed as FSBO, or homes that sellers are thinking about listing.