How can one who has trouble concentrating during Shemonah Esrei train himself to overcome this problem?
If a person cannot concentrate during Shemonah Esrei, let him choose one bracha and study from some worthwhile sefer what that bracha means. Otherwise, you don’t know what you’re saying. Not just the teitch but the real lessons of that bracha. The Siddur is one of the great opportunities of life. But you have to know the Siddur in order to make use of this opportunity. The Siddur is a very profound book, so you must find a sefer that explains the Siddur clearly and take one bracha and study it well. And then practice that one bracha every day until you are able to say it properly. And when you become perfect in that one bracha, then try another one.