What I did to take long exposure pictures was to put my settings on ISO 100 F 5.6 and 5 seconds for exposure which can vary depending on what you want for your photo.
Before you take a test shot, make sure your camera is focusing. You need to be in a dark space using only the led lights or fiber optics. If your camera is not focusing change the focus to automatic click the shutter and once it focuses lock the focus by changing it to manual.
Make sure to put your camera in a tripod and have someone else help you with moving the LED lights from one point to another, from left to right or up and down.
Count 3, 2, 1 so the person that is helping you know when to start and once you started don’t click anything in your camera.
Look at your picture before taking more photos and make sure you are getting good lighting in your photos.
If you want to learn how to improve more your long exposure photography make sure to read photographytalk