Here is the best way to set up a system with a small system drive and large data drive.
1.
Move all your User Library folders to D:
Open Windows File Explorer
In the right hand pane, right click your Documents folder and choose Properties
Select the Location tab
In the Location box, type D:\Documents then click Apply and OK
Please Note, you must specify a folder name like D:\Documents, not just D:\
And before you move another folder, you need to wait for the previous folder to move completely.
When that move completes, do the same for Pictures, Videos and Music
Each time, provide a new folder location, for example, Pictures will go to D:\Pictures
2.
Move the location of all future content downloaded from the Microsoft Store
Open the Settings App (gear icon on your Start Menu)
Go to System - Storage - Advanced Storage Settings - Where new content is saved:
Change all options you find there to D
Also, for any Apps or games that you may have downloaded, go to Settings - Apps, then select that game or App and there may be a Move option.
3.
If you are a Steam Gamer
Stop all processes associated with Steam
Move the Steam folder to your D drive manually
Then open the Steam Control Panel and point that to the new location