Hmm. I think you might be getting at two different questions.
One: How do you get better at systems design? Build stuff -- lots of stuff. If you're interested in designing particular kinds of systems (say, planet-scale web services...), then get a job at a company that does that kind of thing.
Two: How do you get better at systems design interviews? That's much easier; you can just throw money at the problem. Use one of those paid mock-interviewing platforms where you can hire FAANG interviewers to anonymously interview you and give you feedback.
I just went through this interview prep and got the offers I wanted, so I can offer you a data point. It took me < 20 mock interviews (total cost of < $10K) to go from "I have no idea what I'm doing" to "I'm not worried about this part of the on-site interview loop." Admittedly, I have a decent bit of experience architecting systems at scale, so I was mostly using this approach to refresh my memory (heading back to a Big Tech job after several years of retirement) and get familiar with the interview format.
There are some common resources recommended for this sort of thing if you want to also make sure you've read the right content. The most helpful resources for me were the DDIA book [1] and the "Systems Design Interview" YouTube channel [2]. Both are great for breadth and getting exposure to a ton of different concepts -- after that, you can follow your nose (or the book's bibliography) to get depth on whatever you're most interested in.
Good luck with it! It's a deep and really fun rabbit hole. I suggest you find a particular type of system that you're really interested in; start pulling on that thread, and you'll inevitably find your way to all kinds of other fascinating systems-design topics as you go.
Most people can't casually throw away 10k to get better at interviewing...
I'd say for us non-wealthy mortals, the best approach is to find another engineer who will conduct mocks for you. Short of that, maybe do one or two paid mocks to calibrate yourself, then practice on your own.
The sad fact is the "system design interview" is not really like actual system design at all. It's more about following a specific format that everyone expects and knowing the ideal solution up front.
One: How do you get better at systems design? Build stuff -- lots of stuff. If you're interested in designing particular kinds of systems (say, planet-scale web services...), then get a job at a company that does that kind of thing.
Two: How do you get better at systems design interviews? That's much easier; you can just throw money at the problem. Use one of those paid mock-interviewing platforms where you can hire FAANG interviewers to anonymously interview you and give you feedback.
I just went through this interview prep and got the offers I wanted, so I can offer you a data point. It took me < 20 mock interviews (total cost of < $10K) to go from "I have no idea what I'm doing" to "I'm not worried about this part of the on-site interview loop." Admittedly, I have a decent bit of experience architecting systems at scale, so I was mostly using this approach to refresh my memory (heading back to a Big Tech job after several years of retirement) and get familiar with the interview format.
There are some common resources recommended for this sort of thing if you want to also make sure you've read the right content. The most helpful resources for me were the DDIA book [1] and the "Systems Design Interview" YouTube channel [2]. Both are great for breadth and getting exposure to a ton of different concepts -- after that, you can follow your nose (or the book's bibliography) to get depth on whatever you're most interested in.
Good luck with it! It's a deep and really fun rabbit hole. I suggest you find a particular type of system that you're really interested in; start pulling on that thread, and you'll inevitably find your way to all kinds of other fascinating systems-design topics as you go.
[1]: https://www.amazon.com/gp/product/1449373321/
[2]: https://www.youtube.com/c/SystemDesignInterview