GMAT Strategy

I received a PM asking me to comment.

It's great that you're paying attention to your weaknesses in terms of process - a lot of people overlook this.

Stamina / concentration may be an issue for you. You mention doing 25Q per day - do you do them all at once? Or do you check answers in between or take other breaks? It's a good idea to do them all at once and only go back over them after you're done with the set. That will also give you practice with managing your time over the length of a longer set.

Also, during the test, do you get up and walk around on the breaks? Do you have something to eat and drink? What are you doing to get yourself "pumped up" for each section?

You didn't actually mention this, but I assume that you are timing yourself when you do these problems, right? If not, start doing so.

Start keeping an error log in which you record precisely why you got any problem wrong. Then figure out what you need to learn, how you can change your methods, and / or how you can change your habits in such a way that you minimize the chances of making that particular mistake again.
If you aren't being as systematic later in a section, what specifically aren't you doing that you do when you are being systematic? Where are things breaking down? And, then, what can you do to keep your habits going for the entire section?

Don't forget that, sometimes, what you will need to decide is, "This problem is out of my reach.  My best approach is to make an educated guess and move on."  Then figure out how to do that.

When reviewing problems, you should be able to answer these questions:
For ones you got wrong:
1) Why did I get it wrong (as specifically as possible)?
2) What could I do to minimize the chance of making that error (or those errors) again?  How will I make whatever that is a habit so that I really do minimize chances of making the same error again?
3) What are the right / best ways to approach it?
4) Of the right ways, which one is the best way for me (combining both efficiency and effectiveness) given my strengths and weaknesses?
5) How will I recognize problems of similar type in future so that I can apply that "best way" to the problem?

For ones you got right:
1) Did I really know what I was doing or did I get lucky?  If I got lucky, review all of the "wrong answer" questions, above
2) If I did know what I was doing, did I also do it in the best way (for me)?  If not, figure out the best way for you.
3) How will I recognize problems of similar type in future so that I can either repeat my original success or apply my new "best way" to the problem?

Also, Jim is so right that we need to study why the wrong answers are wrong - this is critical on verbal! For any question (whether you got it right or wrong), be able to articulate:
- specifically why each wrong answer is wrong
- which wrong answer is the most tempting and why
- how to recognize that the tempting wrong answer is still wrong anyway so you can eliminate it
- why someone might be tempted to eliminate the right answer