As it's your first attempt I feel it is wise to not critique too heavily. The fact you got out there and tried is what matters.
When it comes to night photography something I've found in cities is that sunset to around 45 minutes afterwards is that prime light. After that the sky starts to look too black and it ain't worth it.
Photo 3: Nice composition and the cyclist is a nice addition. What could be improved? I would avoid having people half cut off on the sides of the images. Not at all easy in a city where it's heaving with people. I was in London last Friday and Saturday and from the view I had I could see the madness on Westminster Bridge. The Elizabeth Tower (Big Ben) is nicely positioned but what you could do is kneel down and see if you could avoid having the trees cut into the top of it.
Photo 5: This has one thing missing which is the sky. It is what I said about that prime time for capturing a city at night. At the moment sunset is around 425PM in London. By around 5PM any decent light is gone. Could you go back? If so, definitely try and get it again!
Photo 6: Done this before and it's always nice having those lines lead you in. What's wrong? The bottom is underexposed and needs lifting if you can. But otherwise on the right lines.
Photo 7: Undecided. It kind of works. Even though it's quite dark there is something about it. Again, I suspect it's the time it was taken.
Photo 8: Now this is where it picks up. Leading lines are near perfect here. Is black and white doing it justice? Without seeing it in colour it's a hard call. Otherwise it's the light again. Being hyper picky I would prefer the people a little closer but that's it.
Any help?