Hmmm. There are a few different levels of "proficiency" for a product as sprawling as AWS, and I think there are different ways of approaching each level. You didn't tell us what you are looking for :) .
* Broad knowledge of services. This is important because you can often short circuit or accelerate entire projects just by being aware of AWS services. Ways to learn this: certs (esp the Architecture cert), subscribe to rss feeds, sign up for https://www.lastweekinaws.com/newsletter/ , read: https://expeditedsecurity.com/aws-in-plain-english/
* How to use a service at a basic level. This means that you know what a service is/does and can do basic tasks with it (start up an EC2 instance or know which EC2 type makes sense for a certain use case, for example). Here the AWS tutorials and other docs are good (reference architectures, well architected framework), as are the certs.
* Understanding the ins and outs of a service. This is where you start to dive in deeper. You might learn what the limits of EBS are for certain EC2 instance types, how to use local volumes, how to maximize network throughput, when you might use dedicated hardware, etc. Here good sources are books, re:invent videos, the builders library: https://aws.amazon.com/builders-library/ , hard knocks/testing ( when in doubt, test it out: http://www.mooreds.com/wordpress/archives/3335 ). You can also short circuit some of the learning by hiring consultants.
* Being an expert at a service. I'm not there, but I've definitely seen some of these. The best way to get here is to do lots of projects. You can also try to teach others about this by teaching courses, writing a book or video series, or blogging. I find that teaching something causes me to learn it in ways that doing that same thing never does, because you have to be prepared for questions.
Source: was an AWS cert instructor for a couple of years, have used AWS for over a decade.