nether; especially fortresses at intersections or corners i pace a piece of cobblestone and a torch in the direction of the portal. for points of interest like a blaze spawner i place arrows on the ground with torches. 4 torches in a row with two torches (for arrow head) poining towards the spawner.
regular world caves; i place a piece of netherrack and light it near major exits to make them easier to find; for dead end caves i mine resources leave torches in place then seal the entrance with dirt and place 2 torches together to signify a closed cave; i also use torch arrows like in the nether to point towards exit
nether; especially fortresses at intersections or corners i pace a piece of cobblestone and a torch in the direction of the portal. for points of interest like a blaze spawner i place arrows on the ground with torches. 4 torches in a row with two torches (for arrow head) poining towards the spawner.
regular world caves; i place a piece of netherrack and light it near major exits to make them easier to find; for dead end caves i mine resources leave torches in place then seal the entrance with dirt and place 2 torches together to signify a closed cave; i also use torch arrows like in the nether to point towards exit
any ideas you use for exploring extensively?