If I was in this situation, I would find a topic that I know quite a bit about and which the other person is interested in. This creates a common ground and you can ask a lot of questions.

I also find that creating hypothetical situations and then asking "What do you think?/What would you do?"

For example, I was talking last night to an aircraft engine tester. I asked him, "What happens if a flock of birds enters an engine, how do you test for that?". His answer was very interesting and led to further questions.

Hope this helps!

Nicholas

It is strongly advised you had better prepare best for the worse, which is the only tip to ensure the conversation with people in the party is cheerful and pleasant. Think about who you are going to meet and what topics you are likely to approach such as his occupation, hobby, family, country or anything you may relate to these people then you would become a conversation expert. 

However, if your English proficiency is not good enough to associate all situations at the scene to the database of your head, instantly, quickly and effectively, you might have to work more on your English speaking and writing practice before you can have good command of the conversation.

Considering your English level in lines, I think what you need more is to simply make your speech more interesting and intriguing. You may do more study on local culture and local community through intelligent  observation. 

Personal perspective. Hopefully that is useful.

If that's a choice, just talk to people with whom the conversation goes on forever without any effort (e.g. ones you have things in common with).

If they're clients and you can't choose, if you can't find a shared interest, then ask about their interest and they'll keep talking. If you want them to like you, then this is a better way than talking about your interest as Nicholas suggests.

How To Win Friends And Influence People is a great book for this.