If you know where you're going, but don't have a very good idea of what's there (aside from the obvious), you're in danger of getting bogged down in tourist traps, because they're always easy to find. It helps to educate yourself a little before you arrive.
Talk to your travel agent. Tell your agent as much as possible about what you want and don't want from your vacation. At this point, you're researching your options, not buying. A good travel agent will help you do this: Though it's not really what they're paid to do, conscientious agents are always gathering information to pass on to clients.
Read up. Guidebooks (even older ones) are helpful for giving you background information about the history, culture, and political situation of your destination. They can also suggest stellar sights. Just make sure you pick one that seems to address the kind of travel you want to do, and whose suggestions are in accord with your budget. There are a growing number of individual books and series aimed at the independent or budget traveler. Check your local bookstore or library (also good sources for travel-related periodicals).
Tourist brochures can also be good resources--they'll tell you where you don't want to go (because everybody else is likely going there). Publications of various national tourist boards can be used in the same way.
Talk to people (part 1). Other people are, without question, the best source of offbeat travel gems. Find out if anyone you know has been where you're going, then ask them about it. What did they like and dislike about where they stayed and what they ate, did, and saw? Get online and find chat rooms and message boards about your destination (most major search engines have these services--type in "travel message board" or "travel chat" to find them).
People's travel preferences vary widely, so try to find out whether your source's biases (and budget) match your own. Personal anecdotes are not always reliable on the details--try to verify such information with another source before you make plans based on it.
Note: It's helpful to remember how travel agents are paid: They get a commission from airlines, hotels, tour operators, and other travel service providers. Be wary if your agent seems to be steering you toward choices that don't really suit your needs or budget.
Even good agents will mostly be able to book you into only the biggest, most expensive, and most "touristy" tours and services. Most of the more modest, local travel service providers don't have the wherewithal to reach foreign travel agents, much less offer them commissions.