Most important is to choose an experienced Realtor whom you feel you can trust; referrals are a great way to find somebody who you will be happy with. A competent and professional Realtor should be actively finding you potential homes, keeping you informed of the entire process, negotiating on your behalf, and answering all of your questions with competence and speed.   

First, it is important to find an agent who represents YOU and not the seller. This is extremely beneficial during the negotiation process. If you are working with a Buyer's agent, confidentiality is key. The fiduciary responsibility of the real estate agent is to the Buyer. In addition, he or she is also focused on negotiating the lowest PURCHASE price.   

Also, when using a Buyer's agent, more properties will be made available to you. In most cases the real estate agent is a member of his/hers local Multiple Listing Service, as well as having greater access to properties that may not currently be on the market.