Alignment can be one of the biggest challenges in learning how to role-play in character. A player's character will, most likely, be very different in personality and POV than the player themselves. Some choose to do an accent or take on a verbal or physical tick to distinguish the character from the player. Internally, you have to evaluate every potential game decision the party encounters, ensuring that you don't lose focus on the character by thinking strategically about the game rather than acting as your character would most likely act. It is tough enough when the party make up hovers somewhere between Lawful Good and True Neutral, leaving the "evil" alignments more to the creatures and villains the party will face. What happens if you have a player who wants to truly go the dark side in your adventure or campaign?
If I have to pick a single rule book as my favorite from the Dungeons & Dragons library, I always go with the Monster Manual. I'm quite partial to the art within, especially those vintage David Sutherland and D.A. Trampier drawings from the original AD&D edition, not to mention the vast menagerie of potential foes for PCs. I have to admit that many of my favorites are criminally underused, with only a happy few DMs daring to run those off-the-beaten-path creatures in a game session. Now that I'm finding more opportunities to be the DM, I have returned again to these hallowed pages, mining through them for interesting encounter possibilities. Turns out, though, that you have to take care not to bite off more than you (or your PCs) can chew.