From your statement about taking the next step in the welding field implies that you have the necessary experience to sit for the CWI test. Approximately 20 years ago, the thing that benefitted me the most for my CWI test was going to the prep course that the AWS offered. I spent 5 days at an AWS prep course at a hotel in Houston and took the test on Saturday morning while the information was still fresh on my mind. I, too, wanted to pass it on the first try, which I did. There is much reading material out there and many home courses that will benefit you, but the prep courses go over everything that is on the test. Some prep courses even guarantee you a re-test at no charge if you fail it the first time. If this is the path you want to follow, be prepared to pay a fair amount of money for this 5 day course, but it was worth it to me. You will be receiving many more suggestions from other people giving you advice on what worked for them. I suggest you heed all the advice you will be getting and decide what is best for you. These are a great bunch of people (welders, QC, Welding Engineers, etc.) that participate in this forum that are willing to share their ideas with you; all of it given in the best of intentions, so pay attention to all of them. Good luck.
Chuck