Good machine.
Match the bobbin tension to the top thread tension so the thread interlock is pulled into the center of the fabric.
That will give you the strongest stitch with no bunching or loose areas.
Use good needles, old dull or corroded needles tear thread and fabric.
Oil the machine. Oil is your friend.
I have "fixed" poor sewing problems by just oiling everything.
The old New Home machines from the 60s have some of the best stitch quality out there even today.
I have an old suitcase Singer machine that works well still.
A #7 Singer that is a beast. It sews leather, parachute rigging etc. Just the machine w/o motor weighes over 100lbs.
The old peddle machines are great, they will sew heavy fabrics and some leather too.
Sewing machines that do a complex operation, they are cool!