What a great concern you have! Are you in Korea now? You are referring to Korean friends?
I guess yes. Actually you are asking how to start a good conversation and have fun talking with them.
Even native speakers have trouble making a good conversation. I guess many aspects of having conversation depend on your 'personality' or 'character'...
Normally, be respectable and be formal in the beginning.
Depending whom you are talking to, gradually speak in both informal and formal. (REMEMBER! People are very different. You want to have a good conversation with anyone!?? Always find out what types of person is... such as is he/she outgoing, conservative... efc)
You are a foreigner. So don't worry about your language too much but, you have to watch your action/attitude toward them(Korean).
Your action speaks louder to them. Be flexible and focus on their interests (NOT YOURS).
If I clearly explain about this, I should publish a book about this kind of topic.
Even though I consider myself as a good speaker, even for me, it's hard to lead/start conversation with some people (especially with strangers).
(Best tips: #1 - it's not about YOU, #2 - people are different, #3 - have fun)