There is a very natural place to ask for a response in the middle of the bi-lingual Gospel tracts. The JESUS video gives the viewer an opportunity to respond after watching all of Luke's Gospel. At evangelistic parties you may ask people to fill in comment cards. 

When talking with people whom you sense are ready to respond ask: 

"Have you ever asked Jesus to come into your life and forgive your sins?

"Would you like to do so now?

"Could you say the following prayer to God and mean it? 

If they respond postively you are ready to begin  Follow-up

Tell us about your experiences with Encouraging a Response

How do you judge when is the "right time to ask for a response?  
How much do you tell a person before asking for a response? 
What do you do if the person does not respond positively?