Many harbours have a mass of lights, neon, traffic, street, discos, fish and chipperies all lit up so that buoys and leading lights can be quite impossible to see against it all.
If you look at the large scale chart of your destination port, you may well see that some approach directions are much better than others. If the layout makes it possible, plan your approach so that the harbour lights are not in line with a mass of light. You should then pick out the leading lights or buoys you want more easily and hold them in view even if you have to follow them into the area of brighter light. Given time and the right situation, I always enter Plymouth via the western entrance to the breakwater, because the marks are far more easily seen against the backdrops of Maker Heights, Staddon Heights and above Jennycliff Bay rather than via the eastern entrance which is directly in transit with Plymouth lights.