Does Thanos just instinctively know how to use the Infinity Stones or was he preparing beforehand?

aka the “you’re not the only one cursed with knowledge” quoting him talking to Tony Stark.

This is a decent indication that Thanos has done his homework.

This is further supported by essentially everything we see Thanos do. He never seems to lack a plan, he always knows what the next step is. We see him interact with many different people in many different locations, and he's well aware of his surroundings and the people he deals with.

So, yes, having studied the stones is a reasonable possibility.

Also note that Thanos is surprisingly able to hold the Infiniy Stones, which suggests that he's more capable than the average creature to hold the stones, and thus likely also has an innate aptitude to wield the stones.

However, there is a more interesting possibility here.

There is precedent that items which hold a stone are easier to handle than stones themselves.

• Red Skull is able to use the Tesseract as a power source.
• Loki is able to wield the staff he got from Thanos in the first Avengers movie (which houses the mind stone) with relative ease.
• Ultron is able to use the staff as well, when he mind controls Helen Cho in Avengers Age of Ultron. This is an interesting point, as we effectively have a machine wielding an infinity stone.

Similarly, Thanos has a glove which is specifically made to house the stones. It's plausible that the glove helps streamline the wielding of the stones. This could be indirectly be confirmed by the glove being severely damaged (and seemingly broken) after Thanos snaps his fingers at the end of Infinity War.

Just as an example, notice what we definitively know exists:

• Tools can be made which house the infinity stones and encase their power so you can safely wield them.
  • As is proven by the many objects which house(d) Infinity Stones.
• Tony Stark has developed technology that allows him to control things using his thoughts.
  • Thanos is the most resourceful person with far-reaching access. If Tony Stark can develop thought control devices, so can Thanos.
• Weapons created in Nidavellir possess abilities that are ableto make accurate judgments. For example, Thor's hammer seems to be able to intelligently decide whether it should resist movement or not. At the end of Age of Ultron, Tony/Cap specifically argue that the hammer lets itself be carried on an elevator, arguing the point that it's a very intricate rule system.
  • It stands to reason that armor forged in Nidavellir can have the same properties.
  • If Ultron, a machine, is able to wield the staff; then it stands to reason that an object can be crafted which is able to use/direct the stones' power.

Combining these facts, it's perfectly plausible that the Infinity Gauntlet can read Thanos' mind and intelligently operate the stones to do what Thanos is thinking about.

I can't prove that this is the case, but I do think I have proven that all needed components for this technology have individually been proven to exist and therefore it is a reasonable conclusion to draw, given Thanos' broad access to resources across the universe.