In most states, it takes just 60 or 90 hours of education to get your real estate license.  And those classes don't really teach an agent how to successfully market and sell a home, just the basic concepts and a legal overview.  It is hard to think that someone you entrust with your largest financial investment may not have the training and experience to create the optimum results you are looking for. 
For this reason, you want to hire an agent that as demonstrated their commitment to continuing education in the real estate field by obtaining professional designations and certifications.  A sample of these follow:
ABR - Accredited Buyer's Representative
ASR - Accredited Seller's Representative
SRES - Seniors Residental Specialist
GRI - Graduate, Realtor Institute
CRS - Certified Residential Specialist
CNE - Certified Negotiation Specialist
MCNE - Master Certified Negotiation Specialist
CSP - Certified Short-Sale Professional
Be sure and ask your agent if they have any professional designations, as well as how many homes they sell on an annual basis (ask for a printed list).  Agents hone their skills and market knowledge through home sales, and if an agent is part-time agent or not very active in the market, they will likely not have the knowledge or skills to get the best results for you.
It is also very important to ask your agent their level of negotiation expertise.  After all of the hard work you put in to getting your home ready for the market and attracting the right buyer, you don't want to lose a sale because your agent doesn't have advanced negotiation skills.  The new designation, Master Certified Negotiation Expert (MCNE), requires a high level of advanced training, providing an agent with the skills to create the best outcome possible in offer negotiations.  Only 180 out of 1.1 licensed agents in the United States have this designation.  Of all of the designations listed above, this is the one that could make the most difference to you in getting your home sold, and for top dollar.  Ask your agent what their negotiation style is - win-win or win-lose.  A good negotiator will have a collaborative approach, where both parties feel 'medium ground' was reached and everyone is happy with the outcome.