Here's a topic I'm interested in, and guilty of as well. When I was at Denver Seminary I taught beginning Koine Greek for two summers to fellow students. While I was at Trinity, I taught it for two years as well. However, since I finished my doctoral work and am teaching in a different field, I have let it slide.
So the book, Keep Your Greek by Constantine Campbell is both a challenge and a resource for keeping or regaining one's Greek skills. Given that seminaries require a great deal of time, effort, study, and money to raise the skills of their students to a certain level, it is worth students putting effort into keeping these skills after they finish their seminary studies.
However, it is not always easy to do so. When I finished seminary (twice) I ended up back in education in a different field, and even when I taught Bible and related subjects, a knowledge of Greek was not really required. So too, I imagine, for many pastors. The demands of their vocation allows them to not use their language skills, and so over several years, their skills deteriorate.
Campbell's book is available both at Zondervan and through Amazon in both paperback and kindle editions. This or a similar book should be required reading for those who are in the final stages of their seminary studies.
The book is fairly short. Each chapter is dedicated to one topic, ending with excerpts from Campbell's blog on the topic. There are ten chapters, plus an introduction, appendix, and a list of resources at the end. The blog mentioned is http://readbetterpreachbetter.wordpress.com/ which has other resources for teaching and preaching. I'll be checking it out as well.
In posts to come, I'll post more about the contents of the book.