Stitch markers and row counters are your friends. And once you have repeated the pattern a couple of times you'll develop a good sense for where you are in the pattern when you have to set it down and pick it up again.
Also, do you know how to put in a lifeline before you tread into unfamiliar territory? Makes it easier to rip back without having to frog the whole thing.
2014 Bobbin Bramble / Brooks B67
2008 Rodriguez Rainier Mirage / Terry Butterfly Tri Gel
2007 Dahon Speed Pro TT / Biologic Velvet