I’ve lived in London my entire life, I adore this city, i cant imagine wanting to live anywhere else, and i have never experience any more trouble than a little bit of light heckling from randy guys at bus stops 0_o
Now about the ‘safety’. Don’t think walking down any street you will be dodging bullets or any other ridiculous crap, the city is beautiful and lovely, but as with ANY PLACE IN THE WORLD, use your common sense. I.e. try not to be by yourself, and if you are by yourself, try and walk in well lit busier areas. the sort of common sense i am sure you apply to walking around late at night wherever you live at the moment.
i have walked around london into the early hours of the morning and never had any trouble, maybe at most some rowdy drunks but nothing major.
it really depends on the area. places like white chapel and hackney are a big problem area for violence. and people say southwark is bad, but i live in southwark and never experience any problem.
research the crime rate in the area you will be in. either way just dont do stuff like stand around with your phone.
and tell someone where you are going.
there are no special ‘rules’ that apply to walking around london. as i said earlier common sense.
on a final note, i have found walking around central london (nearer the thames) is wonderful at any time of the day even at midnight, as it is always so busy and lit up and there are people and cars everywhere i never feel frightened even on my own, i love it!
have fun with your stay!