Magic 8 Ball - 3 minutes of sitting in a comfortable position in a semi meditative state and saying out loud the words that come to mind, and allowing those words to freely associate to each other. For example, I might say “turkey” followed by “Mediterranean” followed by “rocks”. They are tangentially related to each other. The more you do this exercise, the more your brain will be able to freely associate conversations.
Game the wall - spend five minutes gaming a literal wall. You should be able to do this uninterrupted and be able to go through a variety of subjects in a compelling manner. If you can game a wall for five minutes you can game an unresponsive girl for five minutes, and the girl will always offer you more feedback than a wall could.
These are the two of exercises I use before going out to allow myself to get into a loose, social mood, and are extremely effective. It takes practice but over time running out of things to say will never be an issue, and that’ll allow you to reach your next sticking point.