One way to increase your level of enthusiasm is to view an entire day as an enthusiasm seminar. At this seminar you are going to speak and act with enthusiasm. Your enthusiasm will be real. But even though you might not view yourself as an enthusiastic person, during this day's seminar you can be enthusiastic.
At growth and development seminars those attending are willing to try out exercises that stretch their capabilities. At your enthusiasm seminar, view the entire day as part of your doing exercises that will increase your enthusiasm. When you wake up in the morning, as part of your seminar be enthusiastic about being alive and having the entire day as a gift.
When you speak to other people, speak with enthusiasm just for today as part of your enthusiasm seminar.
When you pray and study, pray and study with enthusiasm just for today as part of your enthusiasm seminar.
When you walk, walk with enthusiasm just for today as part of your enthusiasm seminar.
Since you are only focusing on doing this for just today, you won't have to be concerned about keeping this up. You only need to attend this enthusiasm seminar today. Of course, you might find this so beneficial and enjoyable that you will want to have another enthusiasm seminar tomorrow.
(From "Enthusiasm: formulas, stories, and insights" (2002) pp.156-7; available from http://www.artscroll.com)