When I started taking pictures, my first camera above the ‘point-and-shoot’ kind was a rebranded Pentax SLR. It gave me my first look at features such as long exposure and even double-exposure techniques.
Many years later we enter the digital age and all things become easier, sorta. Long exposures need a tripod, ideally a remote shutter release, a subject with a predictable movement pattern, and a camera that can be programed for it. Sorry cell phone cameras don’t do well for this. If there is an app out there that changes this, comment below as I don’t know of one.
The first step in planning a Long Exposure Shot is to take into account what will move (if anything) in the shot while the shutter is open. Examples would be of stars streaking around in arcs while Polaris is centered in the shot. A brief Google Image Search will pull lots of these pictures. Making star trails in the sky isn’t the only use for Long Exposures, Making light trails on a cityscape or highway is also rather easy and visually stunning, again a Google Image Search will provide many examples. I think the best examples of this type of photography are when you can show something that the naked eye viewer does not see by themselves.
One of my favorite examples of this, is this image…

The brightness of the stars is crisp and yet they do not streak across the sky, mainly because they were not asked to. Instead, the photographer managed to open the shutter while the window of the Gemini Observatory was turning. A soft light inside the dome was enough to show the telescope within, and give the illusion the dome is transparent.
On my recent trip to Petit Jean State Park to photograph the November Supermoon I setup my camera and tripod and started taking Long Exposure shots of the trees with the moon as backlight. The results were magical.

This shot was accomplished with an exposure of about one second and then filtered for noise and to bring up low light details. The moon appears as a sun with no details of her face because it is highly overexposed, but the moon is not the subject of this frame, the leaves are.
It takes a lot of experimentation to get the effect your looking for. I took about two dozen shots to get the one above, and several dozen more in hopes of getting a different shot to work out. I wanted to get the chimney of the cabin I stayed in, but instead got something unintended, color of the canopy above the cabin.

While interesting it was not exactly the effect I was shooting for, but it is an interesting effect on its own. I learned many moons ago that what at first glance appears to be a mistake or failure might just end up being fortunate in that it sends your art in directions you never considered before.
I’ll be the first to admit that digital photography has allowed me to become lazy in technique. I can easily take a couple of hundred shots at any given expedition. I can work around this missed ‘F-stop’, incorrect shutter speed, or the wrong ISO in the camera for the shot I wanted to take. And in those many shots I have lots of second chances. It gives me the chance to show my artistic skills in taking the best of the lot. There are some days that even after a first and sometimes even a second winnowing, I still am left with a lot of pictures to look through.

Of course, I don’t have to try and find the money to get 672 exposures developed either. I call that a win. I don’t have to try and wear a machine-gunner’s bandolier of thirty 35mm film cassettes either, the weight alone would be excessive. What I’m getting at in digital work is don’t give up, keep snapping at your desired image and remember that even if you don’t get exactly what you want in the frame, you might well end up with something you can use.