What to do when you can't just socialize? Like your stuck in your own world while out with others in this one.?

I'm usually thinking about what people are saying but never adding my thoughts to the conversation. Sometimes my mind is on other things which is what I guess people ume I am always doing because we've certainly all been there. But these days I have trouble socializing and knowing what to say and what would be viewed as mean or weird or foolish or a great point. I think my subconscious knows because when I am quiet like this I mostly do make good points, but its not enjoyable for me to be this quiet. I want to be more fun and lively. So any advice?