Youre gonna need a few things:
1: Live in an extremely dry desert. Make sure rain is rare and residual humidity is near non existent.
2: Make sure you have no electronic records, civilian grade electronics are not built to last.
3: Build an underground chamber, or use a cave, and is just as dry and at least 3 meters below ground level.
4: Laminate all your papers, then store them in an airtight, water proof stainless steel box, layered with a ceramic coating on the outside.
5: Make sure your tunnel down is stable, reinforce it so it wont collapse.
6: If you do some stone carving, make sure the carving is at least an inch deep and half an inch wide, then in the carving, color with charcoal to make sure it stains itself from the rest of the rock.
7: Hide the entrance, but leave subtle clues like plastic trash and processed metals around the area as a tip of for future archeologists, but that are of no interest to thieves.
With that combo you may have a 1-5% chance of an archive surviving a few centuries to a millennium
