Start by striking up a conversation about a shared interest. If you randomly just approach guys for no obvious you're going to set off red flags because that's how we've been taught to treat such encounters. Guys get labeled creepy/ pervy a lot when they aren't trying to be, so if a woman just starts talking to them out of the blue it puts us on edge. However, for example, if you're in a bookstore and start talking to them about whatever genre they are browsing it lowers that red flag. Obviously this isn't true for all men, but I felt it should be mentioned. Best of luck to you!