“Explicating” is another word for close reading. Here is a site that breaks down the process you need and gives the “cheaters” ways to scan. (Okay, this method is not really cheating–in part because it is labor intensive–but it can help build your confidence and an ear for how to scan. When in doubt, I use this technique to check my “ear” for the line and what is stressed and unstressed.)
Understanding and Explicating Poetry: http://www.uncp.edu/home/canada/work/markport/best/study/poetry.htm