You know it REALLY doesn't matter what kind of machine you are fixing up. New, old, electric, treadle, hand crank what ever. Check the cords if it has cords. If in doubt don't plug it in. That said... I usually clean off some of the 'patina' so my hands don't get all cruddy while I work. If the motor and wires are ok the next thing I like to do is see if it threads up and makes a stitch. If it does, clean that puppy up and sew something. If it seems to need more TLC I seem to gravitate to the worst problem... Some times it is the bobbin area, some times the tension... Some times the outside just grosses me out so much I do a lot of cleaning first. Sometimes the inside is grosser than the outside. Kerosene should melt down the dried up oils - I don't know about using it on decals. If you want to do an all out dis-assembly, you can go on Billy's tutorial. I tend to use a can with a bit of kerosene and paint the kerosene on the place I want to work on. I paint over and over. I stuff a paper towel in to collect. I try to keep it off me, my stuff and the part of the machine I'm not working on at the moment. I do it outside. If a machine isn't all gunked up - well, cheer! Some times things are a bit rusted. A piece of aluminum foil scrunched up sometimes cleans that up. Sometimes it is so rusted up you wonder if it will ever work. I've seen some pretty good clean ups on this board. I have simply replaced rusted parts for good parts because I have a few parts machines around. Not all machines are going to be in your area of expertise. Now days, if it is a new puzzle I try to find a service manual for what I need to fix, read the instructions a hundred times and dig in. I keep a big old muffin tin handy to put things in - put them in order they came off. Take pictures if your camera does close ups. Call DH to loosen the really tight screws - then shoo him out of there.... Brute strength is NOT always an advantage. Remember, if you can read a pattern you can do this.