I use these two handouts early in my inorganic course to outline how to count electrons and assign ligand types in a metal complex. I introduce it early so that I can use the terms "X" and "L" in class. I come back to it and hit it again when I do my unit on organometallics. The "ligands" handout is my interpretation of the MLH Green paper from 1995 (Green, M. L. H., J. Organometal. Chem., 1995, 500, 127-148.). I really only use X and L in my class (and in my research), though I do make use of X2, L2, etc. I ignore the bar notation.
Using this worksheet, a student should be able to count electrons using either the ionic or covalent method for simple transition metal complexes and organometallics.
I hand this out in class and then proceed to do a few examples in class. The examples on the "18 Electron Guideline: A primer" linked from this LO are good examples to do in class.
I routinely ask students to count electrons and assign ligands as X or L on quizzes, exams, and when they come to my office seeking help.
Once students figure out the difference between X and L, most can count electrons just fine. Occassionally, students will count the ligands ionically and the metal covalently (or vice versa), which leads to all sorts of problems. I specifically alert them to NOT do this when I introduce the topic, but some of them have to make a few mistakes before they get it. I would say that 90% of my students can count electrons and assign X and L by the end of my course.