Recommend a Partition for Dual-Boot Windows / Ubuntu?

I'm hoping to get a new laptop over the summer, so this won't be relevant for a while, but it's on my mind. I want to dual-boot with Windows and Ubuntu. I'd like to be able to access my files from either OS, in such a way that they are easily findable from the file explorer on either OS, but don't know if that would require a separate partition for my files or not, since if I only had Windows, wouldn't everything be on the C: drive? And if so, how easy would it be to find my files if they were stored on a different partition? Also unclear where my apps would go, and if I need enough space on each individual OS such that I can download apps to them individually, or if I can really just have the OSs on their own, with the rest of the space dedicated to files, etc.

How should I partition my drive, based on this? The laptop I'm looking into at the moment has 256 GB SSD and 16 GB RAM, and has Windows pre-installed.

I'd like to mainly use Linux, but use Windows if Linux becomes too confusing at something or if there's a specific application I need that's Windows only.