Don't worry about politeness. I never do. Just try not to be too rude. It won't always succeed. Remember, the more people you chat with, the bigger chance of upsetting at least somebody. Just get used to it!

1. Give your greeting to start your conversation. 2. Don't use offensive language. 3. Say 'goodbye' to end the conversation.

Even more polite? Chinese are already so polite, that I almost always feel myself utterly rude in their presence. Just be yourself.

Hi ,here are some conversation starters for you http://www.italki.com/knowledge/page/SMALL%20TALK%20CONVERSATION%20STARTERS.htm

Please, ask him or her, if they accept to chat with you. Explain better when don't understand something.