The entire reason I love photographing birds is because besides butterflies, they are the hardest thing to photograph. Scenics, portraits, fireworks, weddings, underwater, sports and babies are all much easier to photograph because most of them sit still and want to be photographed. Birds are small, far away, up high, moving fast and have no desire to be photographed, making them the supreme challenge. So first off don't get discouraged and be patient. It takes a lot of patience to capture a great bird image.
Secret number one: Plan on heavy cropping. Very rarely can you get close to a bird. A long telephoto lens is very hard to maneuver and it is hard to keep a moving bird centered in a long lens. Almost every decent image of a bird is cropped heavy. An image with a very small bird in the middle of the picture is usually never very good. Birds generally don't have a really scenic surrounding, and since the bird is the subject you will need to crop heavy in order to have an image with impact. This is where lots of megapixels come in handy. You can't crop very much with 6 megapixels, but with 12 or more you can do a pretty decent crop.
Here is an original and a crop of an image to show you what I am talking about.