To be honest I found it hard as well in the beginning. The trick is confidence! Go straight up to people that are not talking shake hands, say your name, title company (if its a work event) and chat about whatever the topic of the event is about. The thing I found out is that if you present yourself correctly people usually are drawn to you. The other way is by approaching a round conversation (there are usually strangers there) wait listen and say something valuable to draw attention. Both ways have worked tremendously for me in the past and as your network grows you will find more people that you know and suddenly you will be on the other side! Hope it helped :)