Hello! I just passed my admin exam!!! Here are my 2 cents. 

Studying for the SF Admin is like listening to your best friend, brother, and teacher tell you the same story with different details. You won't understand by listening to just one person. You need to listen to all of them. 

1) Do the certification trailmix. https://trailhead.salesforce.com/credentials/administrator 

When you're completing the module. Don't skim through the information and skip to the step by step exercise. Most of the valuable information is going to be in the paragraphs. Takes notes and pay attention. Now, if you already did the trailmix and you skimmed most of the info, go back and re-read the topics that are difficult for you.

2) At first I signed up to a few courses on udemy.com. Even though they are full of information, careful with the courses that are mainly "click here, click there, let me show you something." While informative, the test is scenarios and what you are allowed to do. Not "where do you click." Also, many of these videos will spend 30 extra minutes on information that's not coming on the test, which might be good for real world practice but not good if you just want to know what's important for the test. The videos can be a lot of "how to" but not many theoretical explanations. Also, videos could be outdated.

3) After I failed the exam the first time, I did focusonforce.com. It has study guides and practice exams. I liked it. It's a lot of reading so pace yourself. However, it has a lot of explanations but not many "how to" in terms of where you find the information on the org. So it's good to use your trailhead org to see where everything is. The practice exams are good. There are quizzes of the individual sections. They took questions from those sections and created 6 practice exams. You shouldn't take these just once. You should take it many time until you have the idea. 

4) Salesforce Webinars are great. I took one in March and then another one in May. It was different instructors. Even though the power point is the same, both instructors explained things in different way which helps in understanding things better. My critique is that they don't go over Sales & Marketing and Service & Support section. Those are the sections I had the most trouble with. Plus, they give you a discount voucher on your next test.

5) If you don't have time for a 5 hours webinar, the Trailhead Live 30 min. videos are great. A lot of the videos are repetitive. For example, there's probably 5 videos on profiles with the same power point but with different instructors who explain things differently so it's good to hear different perspectives. 

In general, you have to understand the concepts. If you take a practice exam and you see "workflow rule" and you have no idea what that is. Study it. 

This was long but I know that many people are a bit lost on where to start. It helped me studying from different sources.