To introduce a new topic, or change the direction of the conversation, remember all question words: Who What When Where Why How etc. Then combine said question words with any noun or verb you can think of into a logical or illogical sentence. Be a monkey with a dictionary. Then filter out the ones you think of and pick the best question for the situation.
To stay on topic without having anything more to say about it, simply elaborate on whatever you’re saying by stating the obvious if it hasn’t yet been said. Everyone’s mind holds a different context, and stating something explicitly does several good things: it brings everyone onto the same page, it keeps everyone relaxed since there’s no awkward silence, it gives people more time to think about what to say next, and it can trigger mental associations that move the conversation forward.
Storytelling is the best form of communication and socializing, so try to speak in terms of stories (see the movie Lincoln). Stories are good because it sends a message with an example, and it’s entertaining. Focus on recreating the scene, rather than just progressing the plot, and emphasize descriptions related to emotion. Tell the same story multiple times to multiple people–you will refine both the story and your storytelling skills that way.
Questions to Deepen the Conversation
What do you like to do in your free time? What do you like? What do you care about? What did you do recently [that was fun]?
How long have you ___? or I have been ___ for ___.
Where [did you/have you] ___? or I ___ in ___.
What has happened in the news lately? Global, Domestic, Regional, Local? What has happened to you or your mutual friends in the last few days, yesterday, today? What happened earlier–no matter how dull or boring, it is something to talk about: say what you did. Try to describe it more and expand on every detail
Expand on every detail. Nouns and verbs, expand with adjectives or expressions like similes.