Not every piece- that starts to getting boring and predictable. But before a set of pieces, or sometimes I'll introduce a couple in a row.
Tip: Never begin a recital with a spoken introduction. Play first, then talk.
Tip 2: Use humor, or anecdotes. If there is a good story about a piece or the composer, use it. Try to seem spontaneous, as if you are just talk "off the cuff" (even if you material is completely rehearsed)
Borrow Victor Borge lines where necessary.
I very often play requests which people make before a concert, or during an interval, and sometimes I ask for requests as encored. And I almost always say, "I never play requests....unless, of course, someone asks me to do so."
There's also a certain merit in saying absolutely nothing, but just playing- for a very serious or mystical type of programme. If I was going to perform something like Philip Glass' Metamorphoses or Hans Otte's Book of Sounds I wouldn't say anything.