Hi -
Like Margo, I clean out the bobbin area with every bobbin change. I use a makeup brush. I also lift the throat plate and clean under there with the makeup brush with every bobbin change. I try to oil the machine reasonably often. A friend told me I should oil it after every second bobbin and I tried to do that for a while, but that just seems too often to me. So I shoot for after each project, but that's tough for me since I'm usually working on many projects at once, which means that I don't finish them very often.
So I just try to do it "reasonably" often. When I oil, I also take a Q-tip and try to get any gunk out of the bobbin area. I'll also using my stiletto to try to get things out of the narrow groove around the bobbin area. I try to take my machine in every year for servicing, but it usually ends up being more like every two years. That has been fine for me, but that's mostly because the day job cuts into my sewing time. When I do finally retire (still too many years off), I'll probably have to take the machine in more often. But that's a happy thing since it means I'll be sewing more!