Keeping a conversation going can be a huge challenge if you're shy, have difficulty coming up with things to say, or the other person is simply difficult to talk to because they may have the same challenge.
Don't worry, here is a highly effective way to turn things around.
GO ON A TREASURE HUNT
The first step starts in your mind.
It requires you to reframe how you look at conversations from being essentially a pleasant exchange of information to being a "treasure hunt".
With this perspective, imagine that in the mind of the other person is a piece of treasure in the form of an insight, a different way of looking at things, or a potentially life-changing idea that could positively impact your life.
...And the only way of getting to this treasure is by asking questions.
This gets rid of the need to always know what to say and changes your role from having to be a good conversationalist to being a curious and inspired treasure hunter.
Once you embrace the "treasure hunting" mindset, then the next step is to grab your tools and go searching and digging. As such, your primary tool questions.
To do this effectively, get in the habit of intentionally asking open-ended questions as opposed to simply giving your own thoughts and opinions. (You will have to give some of your own thoughts however, if not your treasure hunt will come across as an interrogation!)
The third step acts in parallel with the second and that is to listen, more specifically to actively listen.
This is done by both consciously signaling to the other person that you are indeed listening and engaged by way of your facial expressions, vocal utterances, and body language, as well as by asking follow-up questions based on what the other person says.
By taking the approach of viewing conversations as treasure hunts, you will keep the conversation going without really having to say much. Good luck!