For sure, being team dynamics is a huge part of it. Sucks you've had consistent issues there, only thing you can do is keep trying with different ppl until it clicks (I think going solo sometimes is fun as well).

Yeah, all these things are skills that you get better at with more experience, so they will develop naturally but I think it helps to be conscious/intentional with them!

I should also clarify that this not something you completely plan up front and implement exactly to spec. You want to try to plan stuff in a way that gives you direction and remains flexible. Again, a skill that develops over time.

In my typical workflow, it's a mashup of all this stuff kinda simultaneously. It's like a nested loop (because why not use a nerdy metaphor). Outer loop is project management sort of stuff: broad strokes planning and vision. Inner loop is a development stuff:  finishing tasks, playtesting, and noting ideas for future tasks.

I do the dev stuff for a while, and then it's back to the outer loop to refine the vision with the new tasks/ideas and reflect a bit. Think about stuff like:

• Did the task I just finished/system I just implemented take longer or shorter than expected?
  
• How am I feeling time-wise (and mentally)? How many hours have I been averaging in the last few days, and do I think I can keep that pace, or even do more? (can tell you roughly how many work hours you have left)
• What should the next steps be? (based on current project state and estimated work hours left). What feels super important to accomplish in the time I have, and what feels more like a nice-to-have?
  
• Ok, I should probably work on task x, y, or z next. How long do I think each one would take? Do I want a quick win or should I take on a bigger system?

I feel like I've gotten faster and more accurate at going through that type of flow.  Helps me keep a pulse on the project's overall state and trajectory.

If you're struggling to identify the critical content, you likely don't have a clear vision of what the project is going to be (design issue), or you might be struggling to understand how you'll implement it (development issue), or both. And that's totally fine! Sometimes you'll read the jam theme and a crystal clear vision of your game pops into your head immediately. Other times you have no idea where to start. Ideally you'd be able to prototype mechanics fairly quickly, so you can decide if you think they're fun or not.

Comments like saying the rhythm mechanic "could have been the main gameplay loop... OR just extra frills" and 'I scoped it to “the menus + SOMETHING in game”' points to a lack of vision on this one, and it sounds like prototyping the rhythm mechanic took too much time. Sucks but it happens sometimes.

And yes, if you wanna set time estimates, record in-jam, and review in post, that sounds great. That's more discipline than I'll likely ever have, but again, everyone is different!