Case Interview Help

Hey PYG - this isn't really a question anyone can answer. 

The thing with casing is you first have to get some reps in and sharpen your own skillset. After about 5-10 cases, you'll be able to see where you're strong, where you're weak and what you struggle with. For some, it's quantitative analysis, for others (like me), it's clarifying questions and it could be structuring or diagnosing the case. Once you've shored up all of those skills (roughly around 10-15 case mark), you can then take a look at nit-picky things (how is your overall pacing, are you synthesizing the case susinctly, are you making sure to interpret the financials/quantitative analysis) and continue to refine the skillset. 
 

After this point, you would take a look at more specific cases (non-proift or untraditional cases for McKinsey, Restructuring/PEG oriented cases for Bain, Financial Ops for Deloitte/EY, etc.). 

For most candidates, they take on ~15-30 mock cases throughout the recruitment cycle. So, I'd change the question to how to begin/sharpen the case skills and follow the tried and true approach (CraftingCases, University Case Books, RocketBlocks, Case Coach, and so forth). 

Agree with everything FinesseGod said. In your first 10-15 cases, you'll make mistakes in all the main areas (clarifying the case, initial structuring, communication, quantitative analysis, chart interpretation, brainstorming etc). Once you've hit 15-20 cases, you'll notice the feedback you get is often concentrated in one or two areas - those are your weaknesses you'll have to iron out as you get more experience.