What’s the best way of leveling the bed? Recently I’ve been having trouble leveling my bed on my Creality Ender 3 Pro.  It’s not that it’s hard to level or anything, it’s that it won’t stay level for more than a day or two.  I’ve been leveling it the same way as always with a piece of paper and I’ve been sure to disable steppers.  So if anyone knows what I can do about this, please let me know.
Generally, there is no best way, there are only the ways that work for you.
I use a feeler gauge, mounted on a detachable holder. I home to 0, lift the Z by 1 mm, and then level the bed to the same number on the screws and corners. Then I home back to Z=0 and perform an extrusion test, and if that is not satisfactory, use a different number for the leveling. The number on the plunger does not generally read 1 mm, as there is an offset between the 0 of the gauge and the printer.
When I don't level from 0 or am in a hurry, I usually only alter leveling by doing about 2-5° turns on all the screws to adjust the 0-height via the nuts, using the visual of the printed line as my aide. This only works because I have the experience how a good first layer should look like.
Another typical method that I stopped using once I had the feeler gauge is the paper, but I found it inconsistent.
Do not do these:

Leveling the bed with a level does not lead to good prints - your print bed needs to be parallel to the movement of the printhead, not to the earth!