The idea is simple (and probably used by many), grab a notebook and give it the job of housing all of your lists when getting organized for entertaining. For dinner parties I usually just jot down the menu, but for birthday parties I include the guest list, games and decoration ideas.
What I find most useful about having this information all in one place is that I can look back to see what I served at previous parties. That way I can make sure I'm not always serving the same food to our guests! It's also helpful when brainstorming a menu to see whats worked well in the past.
I recently filled my original party planning journal and had to start a new one. I chose this pretty Martha Stewart journal and added a festive touch with some silhouette vinyl cut outs. It's a great size to take along to the grocery store and looks super cute sitting out on my desk!