You will giveoff positive vibes is your inner state is positive. What you are thinking at any time is visible and easily readable in your body language.
Calm yourself down with breathing before you go out. You can even find great use from visualisations. As you are relaxing just imagine yourself walking down the street in a way which transmits relaxation. See yourself from the eyes of the girls who pass you by. Put yourself in their heads and hear what they are thinking about you
"Wow this guys is cute" (or if you are an ugly monster from hell you can add the word "mysteriously" so it would be
"Wow this guy is mysteriously cute") and that kind of thought including
"I hope he stops to talk to me".
If you knew that the girls were thinking this about you how would your body language naturally be?
Get a clear image of how that would be and notice how it would feel. Now step into the image of yourself and get into that posture. Now your body language will be perfect and your face will betray your inner state as well. So will your movements and gestures.
Walk through life as an attractive man and you will be seen by others as such.
See ya
VM