I have knitted quite a few lace projects in my knitting life, include big shawls like Irish Diamond Shawl and Muir (do click on the links, the shawls are lovely). Luckily, I never messed up too much to use a lifeline. If you are not familiar with it, lifeline is a contrasting thread that you insert in a row, generally below where you want to rip back, so you don't end up dropping massive number of stitches. It's usually used in lace knitting because all the yarn overs and knit togethers make it very hard to pick up the right number of stitches. Some people insert lifeline at regular intervals, I'm much too lazy/dense/ignorant for that.