Addendum

farbmanjake

Just curious, is it common and/or advised to write an addendum for both a low LSAT and low GPA? Or should you really just pick one?

LawyeringForLife-1

There is no straight answer to this without a more expansive picture of who you are and what your story is, but:
If you can make a compelling case about why GPA wasn't great and how it won't be a problem in law school - absolutely do it.
For the LSAT - tough love here, but the cure to all ailments in this area is...a higher score. I don't know what school you are targeting, where you are based on medians etc. However, the LSAT is one of the MOST important aspects of your application. You may have some sort of extenuating circumstance here too that may be worth bringing up. Still, it will look much better if you had one or more bad scores and the circumstance is no longer in play, so you can show a decent score increase. Whether your target score for your school is 150 or 180 - everything you need is here on this website - the core curriculum, the forums, the explanations and comments, the study groups, the proven tutors and the ones that would tutor for free to develop their own skill. There are ways to fix that - take advantage of every avenue available to you.
Hope you succeed!