I read this question, and I tried some long exposure shots myself. Every one of my shots though, is washed out. How do I achieve a long shutter speed while keeping the lighting looking natural?
You still need to expose correctly! Exposure is covered in depth in this answer. What you've done is increase one leg of the exposure, by using a longer shutter speed. Now you need to decrease the overall exposure by the same amount to get back to a properly-exposed image.
So for example, if your camera's exposure meter told you to take a picture at 1/60 s, and you carried all the settings over to manual mode but changed the shutter speed to 1/4 s, you have added four stops of light to your exposure and need to remove them.
You can reduce the exposure through in-camera settings:
You can also try to reduce the exposure by decreasing the amount of light coming in to your lens. There are two ways to do this: