In social interactions, you can intentionally or unintentionally get closer to some members of the opposite sex, but you shouldn't expect the other person to become your lover right from the start. Therefore, you don't have to specifically pick beautiful girls or those you're interested in to start a conversation with, as that would appear too obvious, and others, including the girls themselves, might have negative opinions about it. Hence, you can also casually interact with or greet members of the opposite sex who aren't of interest to you.