Make consistent accordion folds

Mark both edges

Lay a rectangular paper strip flat. Mark the same fold spacing along both long edges, perhaps ⅜ inch or 1 centimeter. Join opposite marks lightly in pencil if necessary. Keep lines on the back of a visible design, or erase them carefully later. Measure from one starting point rather than accumulating a small error from mark to mark.

A narrow cardstock offcut can serve as a spacing guide. Check its width with a ruler, then place it against a reliable reference line. On a long strip, still stop occasionally to check your progress. A slightly angled guide can produce a surprisingly crooked stack by the end of the sheet.

Alternate the direction deliberately

Make the first fold while keeping the strip's long edges aligned. Turn the paper over and fold the next line in the opposite direction. Continue that alternating movement. Firm each crease only after it sits directly against the previous one. You are building a compact stack, not a slowly twisting roll.

Light scoring can help with heavier paper. Use a blunt tool rather than cutting into the surface, since a nicked line can split when opened. Some papers resist folding across their grain. If your trial becomes rough or springs open strongly, change the orientation or choose thinner stock before applying more pressure.

Check the folds for their next job

Open the accordion slightly and stand it on the table. A fan needs folds that remain mobile; a rosette needs ends that continue the folding sequence when joined. Two mountain folds should not suddenly meet at a seam. Plan that connection before trimming the strip to its final length.

Correct an angled fold early, while there are fewer layers to undo. Heavily worked paper often retains a second crease even after adjustment. Use that piece to establish dimensions, then cut the finished version from fresh stock. Write the spacing and intended use on the back of your successful test. Once a strip is folded, its original length is no longer obvious at a glance.