The standard threading on any kind of hardware follows the righty tighty, lefty loosey mnemonic device for unscrewing or tightening bolts, screws, etc.
Which way is left and which way is right?
Holding a wrench at the 12 o'clock position determines whether you are turning left or right. If the wrench (in the most upright, 12:00 position) falls to the left, you are going "lefty loosey." If the wrench falls to the right, you are going "righty tighty."
Another great way to help remember or figure out which way is right and which left is to visualize a steering wheel. A steering wheel turning to the right looks just like a wrench turning to the right. Same for the left.
To loosen, turn to the left (as defined above).
To tighten, turn to the right (as defined above).
In the world of bicycles, there are a few notable exceptions, namely:
- non-drive-side pedals,
- many drive-side bottom bracket cups.