Hey y'all,
Thought I'd share my experience with the GMAT in case it can be of use to anyone. Diagnostic 630 q37 v39 ---> 740 q47 v47 on official exam in three months.
I started studying back in May by taking a class my university offers (although I graduated in 2018). My initial diagnostic through Kaplan was ovr 630 q37 v39, which was fairly encouraging given I'd only put in one week. Quant is def my weak area, especially compared to the super genius engineers that seem to take this test-- shout out to you all for ruining the curve for dumbos like me

For context, I'm a native English-speaking, US citizen, Finance undergrad, career in program management in fintech banking.
The class was marginally helpful, but the geometry I learned definitely stuck. I think I got a lot more by going my own route.
My second practice test was again Kaplan a few weeks later, where I scored ovr 640 q38 v40. I was pretty devastated by the minimal improvement, although cut myself some slack considering I slept very poorly the night before.
I tried to study 1-2 hours daily, 6 days per week. I usually started by reviewing problems I had missed in practice tests or question banks, then moving on to new problems. I also found youtube videos EXTREMELY helpful.
Magoosh and Manhattan have a ton of free videos there, meant to entice you to purchase their programs, but when you consider that there are 10+ test prep companies also doing this, most topics you could want are covered. I would often leverage these videos as I commuted to and from work (many can be consumed without actually seeing the screen). I also practiced using the OG question banks.
My next practice test a GMAT Official Practice test #2. I scored ovr 700 q42 v44. I was ecstatic because >700 was always the goal, and I still had about a month left to study. I'm not sure why I did so much better on the Official practice test. I've heard the math in Kap is more difficult, but I can't say for certain I noticed that.
Over the course of my last month, I stuck to the same routine of reviewing problems I had missed and then working on new ones, watching youtube to learn new concepts and also leveraging GMAT Club heavily for problems I couldn't figure out (Official Practice Tests don't have solutions).
I took Official tests 4 and 6 and scored ovr 710 q45 v42 and ovr 710 q44 v42. I should mention an issue that I ran into during both of these practice tests. As I began the quant sections, I came upon a question both times very early that I knew how to do but just couldn't figure out. I could tell this would be considered an easy question, so this absolutely wrecked my psyche. In one of those practice tests, when I hit this point I straight up stopped the exam. I thought that there was no use in continuing since I had used 5 mins on one easy question that I likely missed. I decided to keep going though, and was glad I did.
That last test was about a week before my actual test, so I assumed I had topped out at 710 (which to me was great!). I was hoping to hit 700-720 on the actual exam, but was nervous after hearing stories of people getting scores way lower than their practice tests.
The day before the exam, I did no studying at all. I had a pit in my stomach for the entire week of the exam too. I never became super nervous for tests in college, but this one got to me.
The day came and I made sure to eat a light lunch and watch funny videos before my test. I arrived and the center feeling nervous, but confident that I had done all I could do to prepare. When I began the test, my heart dropped as one of the first quant questions was an easy work rate problem, and for some reason my brain could never wrap my head around those. Definitely my weakest of the common quant types. I started to panic, much as I did in previous practice tests when I knew I missed an easy question. But, I pushed on anyway with laser focus. I knew it was make or break time I guess and I had promised myself I would finish the exam no matter what just to get any kind of score.
I thought that I had done a poor job in quant. Verbal felt really good. I was so focused and managed my time very well. If you asked me how I performed overall, I would have guessed 680-700. When I hit submit and saw my 740, I felt like crying. I thought it was a mistake. I was PUMPED.
Score Breakdown:
740 (97%ile)
q47 (59%ile)
v47 (99%ile)
IR 8 (yay)
AWA 4 (not super happy about this. I think my essay wasn't long enough)
Looking back, I still don't know why I did so much better than I had on the latest practice tests, but I do know that I set myself up for maximum success by doing literally every tip I saw online (dressing up, plenty of sleep, no studying on test day, words of affirmation, and, of course, lots of previous study to give me confidence).
Overall, I'm just way stoked to have this behind me. It was a long journey but has given me not only a weapon in my holster when applying to B schools, but also self confidence that I can take beyond.
I'm happy to answer any questions and wish good luck to each of you in jour GMAT journey.