As a writer of program notes, sometimes I think to myself "I went to the trouble of writing this stuff down so you wouldn't have to hem and haw your way through it!" Because, let's be frank, a lot of performers are not gifted public speakers and they don't always plan out what they are going to say and they sometimes go on too long. A lot of the time, in fact, I dread that seemingly obligatory speech that precedes the actual concert.
That being said, sometimes a verbal introduction can be very well done. From Greg Sandow's blog, here is how one artist introduced Schubert's song cycle Die Winterreise. What distinguishes this introduction from many I have heard is that it is very personal: it does not focus on rolling out dry facts about the composer and music, something better done in program notes, but rather it reveals the personal perspective of the performers and offers suggestions about how the audience might receive the music. Excellent things, both. If an audience, especially an unsophisticated one as this one was, needs a doorway into the music, then it should be provided.
I recall a concert I attended a few years ago of cantatas by Schütz, Vivaldi and Bach in which exactly the wrong approach was taken. First of all, as the cantata genre is largely unknown to audiences and these pieces were sung in Latin and German, languages unknown to the audience, there should have been program notes with the basic information about the composers and the music. Most of all, there should have been the texts and translations. None of this was provided. Instead, the director of the concert series gave an introduction. But, alas, his introduction said not one word about the music. Instead he mentioned a personnel change (different conductor) and followed that with a lengthy and difficult to hear plea for donations.
I have been to so many concerts where several functionaries spoke beforehand: the director, the mayor, the city manager--and it was always a frustrating experience because it had nothing to do with the music. I realize that sometimes this has to be done as it is a kind of payback to these people for their support. But I think that, in order to spare the audience, it should be kept to a minimum.
Here is another post that the artist I mentioned above, Erica Sipes, put up on Greg Sandow's blog about speaking to the audience. There is some excellent advice there, especially when she says, "keep it short, keep it simple, keep it sincere."
I think that it might also help to recognize that most of our musical training does not equip us to talk very easily about music. This is where a little musicology can come in handy. Musicologists do learn how to talk about music. Their problem is that they have to learn to adapt what they say to the listeners. It must not be too technical! But a little musicological understanding can help the performer to avoid telling the audience things that are misleading or simply wrong. Something I have heard many times!
Finally, if you are truly inarticulate about music, as some great performers are, then you should recognize that it may be better to preserve the magic by simply going out on stage, bowing, and then playing. Don't force yourself to give an awkward speech that no-one will get much benefit from!
I just performed an interesting experiment: if you go to YouTube and type "concert introductions" into the search box you will find displayed a large number of short introductions to pop music concerts and band concerts. Usually, when people post clips to YouTube they leave off the introductory remarks and just start with the music. Ask yourself why this is. I think it is because that, while often helpful (and often not helpful), introductory remarks are inherently ephemeral and fundamentally less interesting and important than the actual performance. To show you what I mean, here is one of the very few clips of introductory remarks I could find that is neither a pop concert, nor a school band concert: