It's frequently been demonstrated that congregations who are looking up at a screen sing much louder (and therefore encourage each other much more) than those looking down at a sheet or hymn book. Operating the slideshow is a simple job but doing it well really helps with our corporate singing and other service elements that benefit from visual support.
During songs, advance to the next slide as we start singing the last word on the current slide
Make sure you stay focused - sing every word of the songs
Remember there are slides for the bible readings and the creed, and sometimes for the sermon or other items.