Hi ARIEN3228,
To improve in Critical Reasoning, you first need to master the individual Critical Reasoning topics: Strengthen the Argument, Weaken the Argument, Resolve the Paradox, etc. As you learn about each question type, do focused practice so you can track your skill in answering each type. If, for example, you get a weakening question wrong, ask yourself why. Did you make a careless mistake? Did you not recognize the specific question type? Were you doing too much analysis in your head? Did you skip over a keyword in an answer choice? You must thoroughly analyze your mistakes and seek to turn weaknesses into strengths by focusing on the question types you dread seeing and the questions you take a long time to answer correctly.
Another major mistake that people make when training for CR is that they do practice questions too fast. To get Critical Reasoning questions correct, you have to see exactly what's going on in the passages and answer choices, and you likely won't learn to do so by spending a few minutes on each question. At this stage of your training, you may need to spend even fifteen minutes on each question, learning to see what there is to see. Here is a way to look at this process. If you get a new job in a field in which you are not experienced, you may not be as fast as the other people working with you, but you know you have a job to do and you make sure you learn all the angles, so that you do the job well, if not as quickly as those around you, Rushing through the job and doing it incorrectly would not make sense. Then, as you gain more experience, you learn to do the same job more quickly. Think of Critical Reasoning questions similarly. Your job is to do what? To get through questions quickly? Not really. Your job is to get correct answers.
So, first you have to learn to get correct answers, generally at least 10 to 15 in a row consistently, and more in a row would be better. That is your job, and if it takes you fifteen minutes per question to get correct answers consistently, then so be it. Only after you have learned to get correct answers consistently can you work on speeding up. Working quickly but not doing your job is useless. Better to work slowly and learn to do your job well. You can be sure that with experience, you will learn to speed up, and then you will still be doing your job well, i.e., getting correct answers consistently.
Finally, a key aspect of getting correct answers to Critical Reasoning questions is noticing the key differences between trap choices and correct answers. Trap choices can sound temptingly correct but don't get the job done. The logic of what a trap choice says simply doesn't fit what the question is asking you to find. So, to get better at your job, learn to see the key differences between trap choices and correct answers.
Regarding resources, check out some of the
success stories of past GMAT students as well as reviews of
various GMAT prep courses to see what prep materials have worked for other test-takers.
Lastly, you may find it helpful to read this article about
how to score a 700+ on the GMAT.