For the inside of the machine I clean everything I can reach with denatured alcohol and cotton balls or soft cloth. Q-Tips for the small places.
As Candace said get rid of the old felt on the drip tray.
For the outside, I use Simple Green on a soft cloth and clean it good. The newer non black machines are painted with paint, not Japaning. I try to keep the alcohol off the outside though. Sometimes the alcohol with clean a streak too well and then you have a tie-died machine.
Leave it open let it air out. Clean the plastic case with what ever you want as long as it's not harmful to plastic.
Let that air out.
That's about all you can do; clean, clean, clean, and air it out.
A lot of the old odors in sewing machines is nicotine. But some is old oil. Some of the older oils were organic and when they get old, they really smell foul.
Joe