Try a few methods out and see what works best with you. In university I studied English Lit, so active reading was very much second nature to me. However, when I followed certain guides that said not to write anything down or underline anything -- which is how I began reading comprehension -- I wasn't doing very well. I went back to the active reading that I was accustomed to: underling, marginalia etc and my reading comprehension, for me, was good: I usually go -3, give or take.

I think the best thing you can do is engage with the material. If that means underlining a few things, awesome. If it means underlining nothing, awesome. Stick to a method that gives you results.

Also, if you don't understand something, re-read it. If a sentence or paragraph is giving you trouble, take the time to figure it out.

I'm in the same boat as you. I feel like I did pretty well on all of the sections save for the logic games. For some reason i got stuck on the second question set, started to panic, lost track of time and had to guess for pretty well the rest of the LG section. I've never felt better about my LR and RC sections though, so I'm on the fence about cancelling.