I took the GMAT a few days ago and I thought i'd pitch in on this VERY helpful forum with my experience.
My score was a bit higher than I expected (I was aiming for anything higher than 680)!
Background
I'm a 25 year old male, from Monterrey, Mexico. I have two years work experience in Data Science and Data Analysis. Studied Economics in Monterrey TEC and earned a 3.5 GPA. I've always been a news-junkie -I have read almost daily the New York Times and Economist since practically high school- which partially explains my high verbal score. On the other hand, even though I have a very quant-ish background, math has always been my weak spot. I think that particularly because of a lack of very fundamental skills, i'm decent to good in DS but awful at PS.
Study Plan
I took a crash course in October-November from a local teacher, and although the material was sub-par, it helped me navigate the format of the exam and learn to find my weaknesses. I didn't really have time or motivation to study during December, but began full-time in January.
Typically I would pick problems from GMATClub, Veritas, OG, GMATPrep, CATs or wherever I could get my hands on and did these without timing (the first few weeks). Every Friday I did a mini-test (quiz designed by me but timed like the GMAT) and on Saturdays or Sundays I tried to do a CAT. I NEVER did less than the entire test, not skipping the essay or IR, so I could build up stamina.
The first month or so I kept an
error log, which was a hassle, but came in very handy to spot my weakness first off. I stopped keeping it towards the last month but by then I already knew what I had to work on.
I guess I would say that the most important factor was consistency. I made it a top priority over anything else to get something gmat-related done every day. I skipped parties and drinking on saturdays because I wouldn't have energy on sunday to study. Even if there was a thing I couldn't miss, I would do a few questions before going to bed or on my iphone while commuting (downloaded GMATClub and a few other apps).
This does not mean overwhelming consistency, but paced consistency. For example, on sundays I would rest in the mornings and start at 2 or 3 pm, finishing by 7 and catching a movie. De-stressing is as important as studying daily.
Tests
My scores varied but are usually in line with what I scored in the official GMAT:
Economist test (mid-december): 550 aprox.
GMATPrep (Jan-15th): 680 (Q: 40, V: 42)
MGMAT (Feb-2nd): 650 (Q: 40, V: 38)
Veritas (Feb-8th): 670 (Q:43, V:39)
Veritas (Feb-15th): 650 (Q:42, V:37)
Veritas (Feb-21st): 680 (Q:43, V:40)
Veritas (Feb-28th): 630 (Q:43, V:34)
Veritas (Mar-3): 700 (Q: 40, V: 47)
Veritas (Mar-6): 660 (Q: 40, V: 38)
Veritas (Mar-7): 680 (Q: 43, V: 42)
GMATPrep (Mar-8): 640 (Q: 41, V: 36)
Official GMAT (Mar- 12): 700 (Q: 44, V: 42, IR: 7)
Crunch-time
It became pretty clear that my weakness was math from the onset.
I concentrated fully on math for the last month, specially on time-management, which was an issue for PS. I guess I improved, but slightly. In hindsight, I would concentrate more on a topic at a time, and not move on if I didn't fully master it, as opposed to trying to just do more math as I did.
About 5 days out, I returned to verbal. I saw very fluctuating verbal scores in my CAT's, so my reasoning went something like this: you can't improve 5 points in five days in math, but you can make sure you score at the top of your scores for verbal and get a good grade overall. It basically worked!
In verbal I went back to my CAT's and re-did the problems I had wrong. I figured out two important things: 1) I was always stuck between two answers: the correct one and another one. When I went back I clearly just picked the other one and got it right. 2) I was finishing with way too much time on my hands (about 10-12 minutes left in verbal). Thus, I took much more time in each verbal question, examining every single word and possibility when I was down to two answers.
Although I was used to doing things "by ear" in verbal (which is not recommended) because I was used to the writing, there are some things that are only true in Gmat-land, such as parallelisms, etc. I found these issues and made sure to pay attention, because at +40 verbal, going by ear (even if you have very good sense of english) is simply not enough.
As I studied, I also made a condensed version of notes -tiny tidbits that I had to simply memorise or that I always got wrong- and so I studied these the last three days. These were NO PROBLEMS, just very concise tips (such as properties of isosceles triangle) or things to note (31 notes for math and 10 for verbal). They also included a mental map of all the things tested in the exam.
Two days before the test I read a few tips on the essay and practiced making two, just to make sure I was following a gmat-friendly format.
A day before the test I had a light dinner, watched some tv and read these notes before going to sleep. I took a small herbal pill to make sure I slept calmly.
Other tips
Learn to say no. I literally put my life on hold during those 3 months because studying for this exam while working is very time consuming. I postponed any appointment till after my exam date, stopped paying my gym and let my friends and family know that I would be totally unavailable.
Tell someone. Sometimes, during those frustrating CAT scores, it really helped me a lot to talk to someone who was in the same situation as me. I studied with my girlfriend, who is also taking the GMAT, so I had HUGE help on that front. But I also regularly called a friend who was in the same situation as me. When your so obsessed with this exam, people who are not in your position won't understand. Try to reach out to someone who will.
Try to "map" the exam. What calmed me down a lot was a mental "map" of the exam I drew. I put in every type of question the exam gives you (Distance, Ratios, etc). This way, my mind was calm because there there was no "surprise" on exam day. Of course, you could be terrible at combinations (like myself) but at least you know beforehand and aren't terrified because you see something on the exam that seems different. This is particularly helpful for an exam like the GMAT because there are only a certain defined type of problem they can through at you.