Locate a seminar speaker or event that corresponds well with what you're teaching. Go to the seminar ahead of time if possible so you can see what the speaker offers and if he/she would be a good fit for your class. You can then decide to either bring the speaker to your class or arrange for the class to attend one of the regular seminars.
Schedule the seminar towards the end of the course. A seminar tends to be fairly thorough when it comes to providing information on a topic and the students will likely get more out of it if they already have a strong background in the subject matter.
Hold a class discussion after the seminar to answer any questions the students have and discuss their impressions of the seminar as a whole and what they got out of it. They could provide feedback that will benefit you in planning seminars for future courses. This also gives you the opportunity to further tie the seminar into your course and tie up any loose ends that may not have been addressed regarding the subject.