Let me preface this by saying everyone is different. So you now can't sue for bad advice…jk
That said, I found the practice SIMs pretty helpful for two reasons.
One–especially for REG–they helped crystalize what tax treatments actually look like. eg NINJA has a great sim for casualty loss and corporate dividends.
Second, you can get a feel for how to fill-out the fields. Although, you can use AICPA (internet explorer only) for that.
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For each exam, I've used NINJA MCQ. For REG, AUD, BEC I also bought the audio files and transcribed those. I made notes out of them. Then as I did MCQs I incorporated explanations into my notes, but in my own words. For FAR, I took notes as I watched BISK/Plus in lieu of audio files.
So, my strategy for each exam was to do a block of 20 MCQ for each of the main 5 or 6 topics. Whenever I get 80% right, move on to the next topic. And, obviously don't forget to review questions. Know why something was right or wrong. It may also benefit you to see the correct approach.
After getting >= 80% on each main topic, I went through each SIM that Jeff highlighted, by topic group, on his list on the main screen when you log in to NINJA MCQ. Incorporate the solutions into your notes, once you put the explanations into your own words.
Then, churn-out randomly selected MCQs, 20 at a time until a week before the exam.
Don't even worry about the trending score. Kinda like if you're trying to lose weight, the number itself is just a guide but you know if you're healthy. It's easy to fixate on it rather than getting comfortable with your understanding. My opinion.
Within a week of the exam date, go through the recently released MCQs, both moderate & difficult.
Then use the rest of the week to review the notes, MCQ and SIMs that made you think.
Kick ass on exam day. For me that is going to a local Panera, DD, Starbucks, a diner etc. early the morning of to just read over the notes. Not to cram but to just lightly review to get my mind right. Then go kick butt.
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Additionally, be honest. If you feel like you really aren't close to passing the exam(s) you begin to study for, TABLE that strategy I just described.
Do not even look at your CPA review stuff yet. They don't exist. Assume you know nothing.
For REG, go to this website to catch-up on corporate & pass-thru (https://tax.cchgroup.com/downloads/files/contemporary-tax-practice/Module4/Topic3/B-Corporate-Alternative-Minimum-Tax-Computations.asp). Hit each module here first. The tax law really hasn't changed that much but mainly use it to help with the mechanics and to better see how to approach the problems. Then, follow the above steps.
For BEC, I felt these two YouTube series really helped catch me up in a hurry: https://m.youtube.com/user/MBAbullshitDotCom? And all of Tony's videos (https://youtu.be/T0sn1tvabXM). He also has free handouts on his site.
For AUD, I honestly didn't need a retool. So, I don't have anything. This exam seems to test most about critical reading than anything else.
For, FAR I would just plunk down the $67 for NINJA Plus. Devote about three weeks to go through every video AND take notes. Rewind A LOT to make sure you write down the examples. This is a steal (Jeff, please ignore this la la la nothing to see here).
Then, depending on comfort level with the material, THEN follow my plan for the exam prep.
It took me about 3 months to study the long way, when I finally passed REG & BEC.
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Sorry to ramble but to answer your question about how to use practice SIMs depends on your needs and comfort level with the material.
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