You can look out for Google's Exam Study guide or get yourself enrolled in a SEM Course to get the best learnings. Sharing my views on both below:
1. Google's Exam Study Guides
If you have surplus time and you are looking for in-depth study, you can refer to Google's Exam Study Guides. You can get these here: https://support.google.com/partners/topic/3204437?hl=en&ref_topic=3111012
These are free and exhaustively designed guides to give you a complete understanding of Google AdWords.
Free and uncut Study Guides (If you are thorough with the guides, you need no other resource)
Time- consuming and wordy guides, giving you all theory to read but no place to practice your learnings.
2. Search Engine Marketing Training
You can take up a complete digital marketing training program or just opt for a Search engine marketing training which guides you and teaches you all essentials aspects of Google AdWords. You can get yourself enrolled in an online course like Digital Vidya's CSEMM course which you can attend from your home and practice hands-on.
Instructor-led trainings will ensure that you are implementing the learnings efficiently. Experts will also share out their experience along with tips and tricks which you must consider to get maximum RoI from you campaigns.
Time-saving as it empowers you the essentials of creating and running campaigns
You need to pay a price for the hands-on learning and expert fees.
If you are planning to appear for Google AdWords Professional Certification Exam, you can refer to link: http://www.digitalvidya.com/blog/google-adwords-certification/ it covers everything you need to know about GCP and clearing the GCP.