I've not done one of these so I guess that I am learning by looking at and criticising your shots. Thanks for the opportunity I think that you need to find an attractive composition, light trails or not, and that first one isn't particularly inspiring. Think sinuous curves, or maybe traffic across an attractive bridge etc. In the second shot the trails appear to be well burnt out, a smaller aperture might have helped there. Then there is the colour balance, tricky in these circumstances, but I'm not keen on that muddy brown look. Like many things in photography, this one is harder than it first appears.
Hi I agree with Bryan on the composition find somewhere on a bridge that you see a nice curve into the distance or a meeting of roads (motorways) with on/off ramps maybe a good looking building in the background. also your white balance is out For these type of shots I usually go for F11, ISO 100/200, in bulb mode, exposures can be anywhere from 10secs to 30sec depending on the available light, heres 3 on my trail shots Clicky Linky and Clicky Linky and my last shot the light trails are not the main subject but add greatly to the shot exifs on the border Clicky Linky HTHs Dave
There is a great deal of colour cast in both images, try shooting in RAW so that you can change the white balance when you get home on your computer when you process your images. This will help to get the colour right, your camera is trying to get it right but with so many different colour temperatures to contend with it cant make up its mind on which is the overall correct one to go for. I have quickly put the bridge shot through PS to get rid of what I can but the motorway image is beyond repair I', afraid.
Good for practice, but as said, the first is a horror story in composition and second is just exposed for too long. Find the right scene first and then shoot all sorts of exposure variation, it is impossible to know exactly what will be best.
Thanks for the comments.. will go back to the drawing board..The images were shot in RAW, I just need to learn how to use it for the best effect.. The reason for the Yellowy/muddy colour to the image is the sodium street lights.. But now I know I can change the white balance both (in camera) and in PS afterwards.. Many Thanks