Ian's dead right, the worst mistake is thinking this is easy. It's not hard but care is needed.
It can be done without an extra pair of hands if you don't keep spares
Tape the 1m rule to your bench. Butt the plastic sheet up to it and tape the sheet's opposite edge to the bench along it's entire length, this ensures the plastic is straight to start with. I tape the two sides as well, we do not want it to move.
Lift the rule. Tape the rule to the sheet and bench at your first set of marks along it's entire length so noooo slipage can occur. With the plastic and rule all taped down, the cut isn't hard. Light pressure on the knife , 3 or 4 passes at least but take as many as you need, heavy pressure will distort the edge and tend to want to move the plastic. Move and tape the rule to the next set of marks and repeat.
This method works well, it does take meters of tape but there's no arguements about who let the rule slip, or who wasn't careful with the knife.
Oh yeah ... use a NEW blade it's worth it, a neat job here helps the fuse go together more easily , and the top strip is of course a 'finish' item that will be seen.