Reading the fine manual and making sure the machine is threaded correctly.
Replacing the needle.
Adjusting the tension, starting with getting the bobbin tension grossly correct, then balancing it with the top tension. <- This is not hard; it's just that most people haven't been taught[0].
Removing the accumulated lint from the bobbin driver and feed dogs.
Lubricating the machine.
If none of those work, have it serviced. If the service person tells you the machine is crap, go to a thrift shop and buy a Singer 66, 99, 15 or equivalent Japanese clone for $25-$100. For a little more money, you can get a 201. A Featherweight is a joy to use and takes up no space in storage, but is much costlier than any of the above options.
Don't buy a slant shank machine (400 or 500 series); that was an evolutionary dead-end. If you absolutely need a machine that zigzags, ask the service person what they recommend.
[0] This is applicable to Singer class 15 machines and their clones, but the general principles apply to any lockstitch machine:
https://ismacs.net/singer_sewing_machine_company/manuals/ha-...
If you have a transverse shuttle (you almost certainly don't) or a vibrating shuttle (you probably don't), you may need to look up information specific to your machine.
We have a few sewing machines that are finicky. Tension goes off rapidly, binds a lot, lint buildup constantly has to be cleaned, clunks mysteriously sometimes. We also have a Singer manufactured in 1899 that just does what it's supposed to reliably (and you can still get parts for it!). Now mind you, it doesn't do fancy stitches or buttonholing or anything but straight stitching and a basic zigzag and you do have to keep the treadle properly lubricated but it even works during a power failure.
Sewing machines, like stand mixers and vacuum cleaners, in the end are power tools as much as radial arm saws, hammer drills, and routers are. It's great to have all the fancy features, but sometimes lowest tech is the best.
I’m also a complete sewing machine noob. We have a sewing machine at our hackspace, someone gave me a minute long tutorial and I had zero trouble with it afterwards. I think the whole “tutorial” was just: follow the arrows when threading it, don’t push down the pedal when your finger is under the needle. And it just worked as it should.
Maybe i just got lucky! But my experience was so different from yours that it made me think that maybe your sewing machine is either bad quality or has some hidden defect.
I picked woodwork, as 95% of the boys did, and about 80% of the girls picked the home-lessons instead.
I do recall doing some sewing lessons outwith the home-ec classes, but it was very irregular. I know I skipped some stuff because my grandmother had already taught me to knit when I was six-eight years old. Only at home did I use a sewing machine, never at school.
I guess it must have been dependent on the school then?
It was useful - I'm quite sure I wouldn't have gotten any exposure to those subjects without it.
Housework, sewing, knitting and stuff I'd been exposed to at home due to a pretty large family already. Though otherwise I would have probably benefited from it, and it did strike me even at the time that it would be best if we could do both classes, rather than having to pick only one.
My overlocker was made in West Germany (when that was a country), and is still going strong.
Threading was a bit tricky the first few times, but the manual is really exceptionally well written.
However, I highly recommend everyone get and learn how to perform basic stitches because hand stitching is a lot hard to get a good quality stitch out of, especially for doing things like repairs in areas that wear.