It is tricky to keep the folds even when you are making the curtains. It is alright if you are using a stripe or check pattern, but with florals or all over patterns it is easy to start folding the pleat crooked. You can draw lines with a pencil but they may show from the outside of the dollhouse.

I have made a grid which you can use to help with this.
To use the grid, first download and print. Turn over the paper with the grid printed on it and put it back in the printer, blank side up. Now print the pattern. The grid will be on the back of the curtains, it is very pale so it shouldn't show after the curtains are folded.

The squares on the grid are 1/4'' x 1/4''