For creative pictures at night you can use either shutter speed or you can freeze the runner with the flash. But I also love to use a headlamp as a source of light; relying both on the runner’s headlamp and a second one, which stays with me. In general, in the night you have to be careful not to use sources of light with different color temperatures. Both flash and headlamps have pros and cons.
It is easier to freeze the runner, but it is more difficult to take a shot without ruining the atmosphere/vibe of the moment. Sometimes it is easier for me to use more than one flash. I have to make sure that each flash is adjusted correctly. Also, a few lighting modifiers (light formers) can be useful; for example, if you want to take some light trail pics. For that purpose, I recommend using a tripod, or at least a monopod. If I do not have one at hand, I sometimes also rely on a stone or tree to position my camera well.
I always avoid aiming the timing light/flash directly at the runners. The short and very bright flashing in the night blinds the runners and they automatically close their eyes. Always stay laterally.
A big pro for me is to see the exposure to the light ‘live’, meaning already before and while I am shooting. The disadvantage, however, is that headlamps operate at a very particular frequency, which is not visible to the human eye. Hence, it can happen that the exposure is good in one shot and, due to no frequency, the next one is dark. You can deal with that by choosing a ‘very slow’ shutter speed and experimenting with that. That way you can minimize the flickering of the headlamp. Try, for example, the shutter speed range between 1/640 to 1/250. For the headlamps, I prefer “Ledlenser”, because they have a relatively high frequency and I can speed up my shutter speed a bit to minimize the risk of in-motion blurring of the runner. Moreover, those lamps can be dimmed very well and have an excellent lighting range. Similar to using multiple flashes, I recommend you also use more than one headlamp. I always like two to three lighting sources to avoid producing a flat light.
Make sure the runner does not shine his/her headlamp directly at the camera, otherwise s/he blinds the camera and your shot will be too bright. This becomes even more relevant for time exposures and the light trails.
Everybody loves silhouettes! They bring a bit of tension into your shots. But the condition for shooting a proper silhouette is backlight. The source of light is usually the sunset, which is directly behind or laterally behind your object. You can, of course, also create your own situation of backlight in your studio, or at home, by placing artificial sources of light behind the object.
It is crucial for a convincing silhouette picture to position the exposure measurement on the background. Only that allows you to create the perfect silhouette, because the object at the foreground remains underexposed. I always choose my exposure manually, to emphasize this effect a bit.
Also, during the day, or in the absence of the sun, it is possible to create a silhouette. Just place your subject in front of the most garish/crude source of light around you. Be careful not to have too many disturbances around your object, that can lead to too much unrest in your picture, and the observer might not understand what the main subject is supposed to be.
Last, but not least, use each type of backlight. If the sun is low, very particular shadows can be produced. But I also really like rain and fog: you can create very cool and exciting moments.
In general, I would say, less is more, especially if you are still a beginner. I recommend focusing on the detail and the composition instead of trying many flashes and lenses. Otherwise you will just be annoyed by the material and will forget about how much influence your own eye has on the perfect picture.
Finally, I am a sports photographer, and I shoot very often in the mountains. Therefore, it is essential for me not to just focus on my photo equipment, but to always bring a first aid kit, and a change of clothes. You never know what will happen and the weather changes very quickly up here. But, nevertheless, I love the mountains, and the natural settings they offer for my shots.
Everywhere but Europe