I like to use charts in knitting, but sometimes I will find a pattern with many lines to the repeat that isn't charted, and I worry about making a mistake if I were to chart it myself. But on the other hand, when the pattern repeat has, say for example 24 rows, it's really easy to get off track and make a mistake. To avoid this, I started using index cards and a little ring (sort of like the ones that are in a 3 ring binder, except they are just individual rings). A rubber band will work too.
Then, I write one individual line along with what line number it is on one card for each line. I punch a hole in the corner, put them on the ring or rubber band in the proper order, and then just flip the card each time I finish a row. This really helps to prevent getting on the wrong row. Also, if I have to stop on a particular row before the pattern is done, I just put a post-it on the card I stopped with and write the date on it. Easy peasy!
(Note--if I am doing a lace pattern where all the even rows are purled across, then I leave the even rows out.)