Hey guys, my new cranks came by mail today and I want to make sure everything is on the right way. So what do I do now?
The pedal on the right hand crank threads on clockwise - the left threads on counterclockwise.
It is very very important that you get it right or you will damage the cranks.
Which way the seat goes should be obvious.
The frame doesn’t really matter, but for cosmetics it looks best to have the slit in the seat tube at the back.
Then you will notice that the pedals are labelled L and R. On many pedals, the L or R is in the end of the pedal spindle. If they are not labelled, then look closely at the threads where they attach to the cranks. The right pedal will have a normal thread (screw clockwise to tighten) and the left pedal will have a left-handed thread (screw anti clockwise to tighten).
The cranks may well be labelled L and R. If not, look closely at the threads for clues. Then very carefully try to screw the right pedal into the right crank or the left pedal intothe left crank. If it doesn’t go in smoothly, do not force it; check the threads again.
Then of course the left crank with the left pedal goes on the left of the uni, and the right on the right.
Also, how do you know what side is left and right on a uni? As long as the left crank is left, and right is right, does it matter what way the frame points?
the cut out is back so it’s quite obvious
huh 
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what cut-off
right under the seat clamp on most unis the is a small slit so it can be tighter
oops sorry, I keep getting frame and wheel set mixed up 
But are you saying the wheel doesn’t matter?
The seat: does matter. Should be obvious which way.
The frame: doesn’t really matter. However, it looks best with the slit at the back. That’s the slit in the top bit of frame tube that has a clamp on it.
The wheel: doesn’t matter. The tyre sometimes matters, but only if it’s a posh one with a fancy tread pattern, and only if you’re riding hard enough to notice the difference.
The cranks: matters a lot. If you get the cranks on the wrong side, then the pedals will unscrew as you ride, and this will damage the threads in the cranks.
Pedals: obviously, they matter. They must match the cranks.
So as long as you have the left crank/pedal on the left of the SEAT, and the right crank/pedal on the right of the SEAT, nothing else matters mechanically.
But to do the job properly, you should really have the frame aligned so that the slit is at the back.
^^+1