1. Use a tripod. I’m usually not a fan of photo tips that start with "use a tripod" because that’s such basic advice—in fact, using a tripod is good advice in almost every photographic situation. That said, with long exposures, tripods are crucial. So start with a good, solid tripod and you’re off to a good start.
2. Use a cable release. The vibration of a hand on a camera can ruin an otherwise-perfect long exposure. That’s why experienced photographers use a cable release, remote control, or even the self timer to put distance between their own unsteady hands and the delicate balance required for a sharp long exposure.
3. Use a lens shade. With long exposures, lens flare can be a little more insidious than usual. It works the same way—with a light source shining directly into the lens creating flare, streaks and color and contrast issues—but it can be a bit harder to spot. In daylight, it’s clear that the sun is the source you have to watch out for. But given a streetscape at night, for instance, there could be dozens or hundreds of light sources that during the day wouldn’t give you a second thought, but at night during the long exposure they become bright enough to flare. So use a shade to minimize the chances of damaging flare.
4. Use a small aperture. If you need to, or just want to, lengthen the shutter speed of your long exposure, start with the lowest ISO available on your camera and then use the smallest aperture available on your lens. This has the added benefit of creating more depth of field, likely a sharper picture, as well as star effects from pinpoint light sources when the aperture is smaller than ƒ/16 or ƒ/22.
5. Lengthen the shutter speed to increase the unreal factor. The longer the shutter speed, the more blurry and surreal moving objects will become. Pounding surf, blowing tree limbs, moving cars...longer shutter speeds mean less natural detail and more unique images.