FWIW, I did absolutely ZERO preparation to install WIN10 on the SSD.
@kevin_hua - so I guess we had the same expeience.
I think alot of comments on this thread are speculation from people who didn't ACTUALLY DO THIS THEMSELVES, they are just commenting. All the BS about windows not installing if the HDD already has windows, was not true for me.
I created a windows install USB from WIN10 when booted from the HDD.
Then I started to remove the HDD, so WIN installer wouldn't complain, but decided "why do all this, just try it!". And guess what, the installer worked just fine, and allowed me to remove all paritions on the HDD and make the drive "empty" again, then select the SSD for installation.
So, in my experience, don't even bother with taking the HDD out or anything, was NOT an issue for me using USB installer created from same machine.