Say hello to everyone you see. Don't wait for others to acknowledge you — acknowledge them first. If you're doing this right, people you already know will be amazed at your heightened friendliness. Strangers will think you are an exceptionally warm person.
Smiling is great, too. If you're intimidated by someone's severe demeanor, smile at him, and try to see his response before turning away. In the final analysis, however, his reaction to your overt warmth is of no concern. Even if only one person returns your smile or hello today, consider your effort a major success. You'd be surprised at how many people you can affect simply by smiling at them.— Alan Epstein in How to Be Happier Day by Day