I keep a spiral notebook on my countertop nearby - I have a page for needles - I write down what date I put the needle in, what type it is and what projects I used it for (some smaller projects don't require a needle change every time but most appliques/quilting do).
I also have a page to track when I last "cleaned" my machine at home.
The book also serves as a quick place to jot down things on projects that don't get finished all in one setting - like tensions, stitch length etc. Another page is a Wish List. Post It note flags mark important things. This way I don't have a ton of loose notes everywhere. I just check my book. I use one of those "journal" type spiral books - they are pretty reasonable and have lots of pages.