I don't always want to do it but I try really hard to clean out the bobbin case area particularly every time I change a bobbin. My old vintage mechanical machine had a couple of oil points but it was very easy to reach them. My current modern machine only wants me to give a precise drop when and where it tells me (mostly at the bobbin case).
I've found keeping a pack of chenille stems (pipe cleaners) with my stuff to be one of the best/easiest tools to use, you can poke it and swipe and get into little crooks and crevices and then pull the lint off it.
As the others have said, I buy oil from the notions wall at the sewing store, there are a couple of brands, a couple of sizes. It's just a drop here and there but the right type is important in multiple ways,