Quick Tip: Keep a log of machine maintenance
When was the last time you cleaned and oiled your machine? Or changed a needle?
You don’t remember?
Me neiths.
That’s why I started keeping a mini notebook next to my machines so I could record when and what maintenance I’ve done. 
I change the needles on my sewing machines fairly often, but on my sergers and coverstitch machines? Unless I break a needle, almost never. And when you can take out your handy dandy notebook and see that you haven’t changed the needles in 5 months, it can make troubleshooting go a lot faster.
When it comes to cleaning and oiling, most of my machines suggest once a month… for infrequent use. HA! For “daily use”, the manuals suggest cleaning once or twice A WEEK. *cough* Oops.
Now that I keep notes, though, it’s a lot harder to say to myself, “I just cleaned them, they’re fine….” I can actually look (in horror) to see that they haven’t been oiled in… well, in a long time.
Since I’m a machine freak and have a fleet of machines, a wee notebook is appropriate, but if you’ve only got one or two, you could just use a Post-it note stuck to the back of the machine to keep note.