First, make sure you have the spark plug wire off before you even tip the mower.
2nd, always tip the mower so that the spark plug is up in the air.
3rd, Think of it this way.
When the BLADE is spinning, it will always be trying to tighten the BOLT.
If it was threaded the other way, the spinning of the Blade would loosen it.
In most cases Lefty loosy, righty tighty.
So counter clockwise looking up at it from the bottom.
BUT, some decks spin backwards, so be careful.