Hi aomundada,
For Sentence Correction:I can't point to any specific guide that I used between my first and last test to boost my verbal. Generally, for someone with a lower score, I wouldn't worry too much about nitty-gritty rules, idioms, etc. However, as you already have a solid verbal score, I'd look at shifting your focus towards more specific and technical rules.
Prep Scholar has some really great youtube videos on the most common idiom errors. I usually reviewed them the night before each test.
You can also pick up some really helpful tips/tricks from other forums on this site. Anytime you come across a really tricky problem, do some digging on this site to come up with a rule that can be applied. Some examples that come to mind: is "everybody" singular or plural, when do I use "could" vs "would," etc.
Again, this is splitting hairs, but when you're already scoring high, getting one additional question correct because of one of these rules can be a huge difference.
For Critical Reasoning:I rarely practiced this as I didn't think more and more repetition would add much value (most of my verbal practice was all sentence correction). However, the best tips that I can give are the following:
Don't fall for answers that are out of "the scope." There's usually one or two basic criteria/assumptions that arguments are going to depend on, so don't let yourself get carried away when an answer choice brings up a third factor.
Try to generate potential flaws in the argument as you're reading it (i.e. if you're doing a "weaken" question, get yourself used to thinking of different caveats that would hurt the argument as you're reading the argument). Then, when you read the answer choices and one happens to match with a flaw that you thought of, you can select an answer much quicker and more confidently.
Again, some of the other forums on here give much more detail and specific questions than I can. Wish I had something more concrete to point you to but hope this helps.