always keep a crochet hook in your bag to pick up dropped stitches. (altho i mostly pick mine up with a small double point).
lifelines can be a real lifesaver if you're knitting lace. every so often, when you know that your lace is correct to that point, take a contrasting color of yarn and a yarn needle, and run a strand through all of the stitches on the needle... leave it there, then when/if you make a mistake you can rip back only to that lifeline!
put all your little doo-dads--tape measure, needle gauge, crochet hook, stitch markers, etc.--in a small pouch, then you can just grab your pouch, grab your needles and yarn and pattern and start knitting!
post it notes are great ways to mark your place on charts. put them from the top, so you can see where you've been!