Scores came back for late June today so thought I'd chime in. My dedicated study period was 7 weeks.
Unlike everyone else here I only took two simulated practice exams (sorry about the lack of data points). Though I did look through the Qs/As for NBME 16 & 18 the week before my exam.
UWorld: Started in the 50s-60s at the beginning, mostly 70s midway through, and low 80s (average) by the very end.
NBME 17: 249 (4 weeks out, after one pass through FA & Pathoma + >50% of Uworld)
'Free 120': 92% (4 days before the exam)
Based on previous students' experiences, it seems like people plateau after the initial learning period, so I didn't feel the need to gauge my progress in a simulated setting again.
Real Deal: 256
I believe I had a fairly easy form, because I felt pretty good walking out of the test (marked <10 on most sections) except for one extremely difficult section where I felt like I was guessing on a bunch of them, even running out of time going through my marked questions. For my mental well-being, I'm really glad I got an easier form. My strategy was to spend about ~1 min/question initially so I had 20 minutes left. In this time I went through every question at least once (tried to justify the answer I chose), and then tackled the marked questions. Doing this, I caught ~2-3 silly mistakes or reasoning errors per section, which was crucial. There's something about seeing a question again after being away for a bit that makes things click sometimes - so if you get stuck, move on and come back to it.
Everyone else has touched on the key points, the most important of which is to get the material down cold when you first learn it in class. The foundation makes it so much easier during the dedicated period. Also, there were 2 questions I distinctly remember from my exam that weren't in UFAP that I only knew the answer to because I paid attention in class. These are the points that matter once you hit 240+.
Besides that, if my 'improvement' from NBME 17 cannot be explained by random variation alone I would have to credit a 2nd pass through FA, and Kaplan Q bank after finishing Uworld (ripped through medium + hard questions in tutor for ~1.5 weeks). Kaplan, while annoying, got me at least a couple questions on concepts that weren't as emphasized or mentioned in UFAP. IMO it's more worthwhile than a 2nd pass of Uworld, assuming one only started using Uworld during the dedicated study period. In addition to the resources I've mentioned, I like to shout out to 'high-yield gross anatomy' which was a fairly readable one stop shop to master a majority of step 1 anatomy. Felt so much better about anatomy after flipping through this.
Best of luck to the next batch of students