I'm not sure this is really a philosophical question, but I think it's about gaining a broader perspective. To take it to an extreme would imply an all-seeing objective perspective. Except for some notions of God, perhaps this doesn't really exist, but some people demonstrate a "broad mind".
"if I see a single mother smoking cigarettes, I will judge that her future will probably be bad."
-- Bad in whose terms? Yours?
My point is that making a judgement involves applying your own circumstances/perspective to someone else's situation, in the absence of better information. That is : prejudice, in the absence of understanding (incidentally I'm not saying this makes a bad person .. the irony of that isn't lost on me .. )
By understanding a situation more, prejudice disappears and the urge to judge disappears. Perhaps the single mother is smoking because she's about to go for a job interview and is nervous, or she used to smoke 20 a day, has cut down to 3 a day and that's what you're seeing.
Another way of achieving this if you can't find out more about the circumstances is to understand the points at which you're applying your own perspective. Try to view the different possibilities of how what you're seeing could arise.
Alternatively imagine it from the point of view of a third person, perhaps from another country or culture, seeing you and the single mother next to each other. You don't know much about the stranger's culture, so you can't second-guess what they'll think about you or the single mother.