Simple stuff like RCA phono cable upgrade, an improved aftermarket phono stage (a necessity for any excellent vinyl playback system), an upgrade of the stock mat, a record weight for added mass, improved isolation feet or an isolation platform (easy DIY project), are pretty straightforward ways to optimize a stock unit.
You can also easily add a few o-rings or orthodontia rubber bands along the tonearm to help control resonance. Adding weighted grip tape (tennis or golf) to the counterweight moves the pivot point closer to center so it requires less force to make it move, which helps make it more nimble.
It’s also pretty easy to undercoat the back of the platter with Flexseal or rubberized undercoating. Adds mass and helps control resonance.
If you really want to take the stock unit further, you can open it up and line the plinth with plasticine modeling clay or Dynamat. Just ensure to keep the functioning parts free to operate. More mass and more resonance reduction.
These are small tweaks that mostly help control vibration and resonance, and help justify a better cartridge that can reveal more information. Most are difficult to even detect on their own, but when summed and working together in a revealing system can make an audible improvement. There are downsides to adding more mass to the platter and by adding strain to the motor, but it has not been a problem over the past 18 months.
My first upgrade was a very good VM95SH cartridge, but after doing all of the above tweaks, I’ve added a Nagaoka MP500 stylus to an MP150 body (and headshell), and it’s now an impressive performer. My other TTs are a Thorens TD124, Dual 1215, Garrard/Marantz w/custom plinth, and several other common decks. The 120X has the potential to hold its own against some very well regarded TTs....getting better sound than this is possible but would cost substantially more money.