Here are a few suggestions:
1. Smile! It's contagious. :-)
2. Pay someone a compliment or give them positive feedback on something they've accomplished (Examples: Great job on that project! ... Thanks for listening. :-) You rock! )
3. Be warm and friendly (but don't overdo it).
4. Remember a random act of kindness goes a long way. You will feel better and the other person will be appreciative.
5. Remember to use eye contact especially when trying to get someone's attention.
6. Think positive and speak in a positive tone. If anyone says something negative, cancel it out with a positive statement.