During the day, you don't have to worry too much. Just don't show you have something of value and dress casual. During the night, I don't recommend going out alone. Except if you look boyish and you can pass for a man.

If you stay in the center (high streets), there is quite no problem. Sometimes some guys try to connect with you, but not too much on the day time. I never go out when it's dark, so I don't have a lot to say about this. I prefer safety over trying.