If a girl is actually sufficiently interested in a guy often there will be signals, ..as a guy, it's upto you to try and notice them.
some girls will even approach a guy and directly hit on him too...
if a girl isn't particularly bothered by a guy, then you tend to get no signals ...or no girls hitting on you ...so you must try and hit on them yourself and see if one will take you.
Like there are some girls, that I'm not into enough to try hitting on them or really make much efforts to impress/woo them...but if they decided to hit on me ... I wouldn't say no.
I imagine girls operate like this to some extent too, but are probably a bit pickier over it being female ....., so if you are not getting any attention from girls either improve your looks, or you are going to have to go around hitting on lots of girls until you find one who "wouldn't say no" ...and hope she doesn't flake out on the date due to lack of interest. Personally, I don't like this method and prefer to try and find girls who show some signs of interest before I go talk to them.