What makes a photo a good photo?no_redirect=1

The image looks flat because you have no shadows in the image.

For example, look at this one (not mine, I just pulled it randomly off Google):

Notice how the shadows give it depth? Look at where the sahdows are. Now look at where the light has to be coming from to make those shadows... That is where your light has to be to make that image.

Or put more simply, a room that is completely and uniformly lit will give you flat looking images. Also, a flash that is mounted right on the camera will also give you flat images because it is just trying to blow all the shadows away.

If you are to the point that you can manually adjust your camera settings to get a properly exposed image, you really should move on to the "People and Portraits" and the "Studio and Lighting" forums. You'll likely get more in-depth discussions there.