Ohh man! I used to watch this movie all the time when I was a kid! Er... that is, whenever I could. I was probably the only kid out of all my siblings who wasn't creeped out or scared by it! xD The French Spider and Centipede were my favorites.
This film goes way(WAY) back for me. And this isn't the first time I've drawn these guys. Although, my kiddie scribbles are long gone, I guess my hand remembered more than I did. lol General practice does help a lot, though! Really understanding shapes and also mimicking styles(but not tracing or copying directing) to the best of your ability will help develop great drawing dexterity.