I rarely ever use the date command, but when I need it I almost always struggle to get the right incantation. So, wrote a blog post for easy reference.
I'm addition to tldr which someone else suggested, there's also the cheat command. It's pretty easy to add to it's cheat sheets, if you have custom commands, or want to keep a specific example. I've never kept a physical cheat sheet... They're just too inconvenient and my fingers are probably already at the keyboard.