If you mean the online test:
Think of it as a merge of a case and the GMAT/GRE.
You need to be clear on some key case-related and account formulas (margin, growth, breakeven, etc) as well as be good at critically understanding the question (including nuance to questions) and parsing through complicated text with a fair amount of distraction.
You'll also need to be good at chart/graph reading.
The (old) McKinsey PST, BCG Online Test, Bain SOVA test, etc. are all quite similar so leverage resources across all of them.
If you mean the regular case
In terms of frameworks
This is a BIG topic and not easily answered!
To be as succinct as possible: the common approach for all cases is:
- Figure out the actual problem being asked - also known as objective. What do we specifically care about and not care about? What would a good answer look like?
- Figure out the key things you need to know to answer this problem - this is like the "buckets" in your framework. What critical information will help you make a decision
- Think + Articulate specifically how each key area will help you answer your question - i.e. "If Item A is big, then I need to look at item B" or "If A is less than X, then I need to check out B"
In terms of case interview preparation
The most important thing here is narrowing down the noise. There is a lot of content flying around, and you need to work hard to focus on what's important (much like when solving a case).
I recommend the following:
1) An initial planning session with a coach: 1 hour with a coach now will have a productivity multiplier effect on all your efforts moving forward. They will figure out what materials are best for you, guide you towards the best ways to learn, and come up with a preparation plan with you.
2) Leverage free resources first: PrepLounge Q&A and case library, Poets and Quants, SpencerTom, Google, etc.). Leverage these options, read-up, and over time you'll get a feel for what you really need and where you really need to invest your hard-earned $
3) Case with other PrepLoungers: Casing with other PrepLoungers is free. Not only do you get to practice casing, but you get direct feedback. Additionally, you learn a lot just from casing others. Finally, from other PrepLoungers you'll learn which materials/coaches are helpful.
In summary, while free options don't beat paid options, you can use them for a while to get a feel for what works for you. Have an initial coaching session to get you on the right track, then go the paid route when it's clear either 1) You are stuck or 2) It's clear the paid route will improve your productivity/progress