Take a moment to envision what your scene will look like, and what parts of it will be stationary, and which parts will be fluid.
2. Be patient and wait for the right time
Long exposures, at their very basic premise, require one of two things to work properly. Either very dim light situations such as the golden hour time periods, very early, or very late in the day – OR modifiers added to the camera to diminish the light that is coming in through the lens.
The reason you need one of these is because leaving the shutter open for longer periods of time, monopolizes one corner of the exposure triangle. When a normal amount of light strikes the camera’s sensor for an extended period of time, you’re guaranteed an overexposure. Therefore, you’ll need to change one of the variables to reduce that amount of light.
The solution? Plan your shoot for very early in the morning, and very late in the evening. The darker it is outside, the longer you’ll be able to leave your shutter open, and therefore the more motion you’ll be able to capture in your image.