It's important that you choose an experienced agent who is there for you. Your agent should be actively finding you potential homes, keeping you informed of the entire process, negotiating furiously on your behalf, and answering all of your questions with competence and speed.
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.