Well, with no additional information, I can only give two advices :
- Like said before, smile to people : smile to those you just pass by in the street, and keep smiling to the people you talk to. Smile smile smile.
- Look at them in the eyes at all times. But keep smiling of course otherwise you will come across as arrogant
Not looking at people in the eyes will make you look very distant.
You'll be amazed to see what a difference these small actions make. It might be hard doing so at first, but it doesn't matter. Just do it a few times, you'll realize how powerfull it is and how much people will want to be closer to you.