From my experience, the non-tricky bits were to use unetbootin a bootable repair-boot memory stick, and use woeusb to make the windows install usb-stick. (I had ubuntu 17.10, and my parter insisted on dual-booting windows 10).
The trickier bits were maybe to deal with my specific situation: ubuntu on a SSD, with home and swap on a 1TB GPT-style hard-disk. I wanted to install windows 10 on unallocated space purposefully left on the HDD.
The first problem was getting windows to install -- it complained it could not install to a GPT disk (which was a bit enraging..). In my case, with an American Megatrends BIOS, the solution to turn off "legacy" video, ie to set UEFI video (whatever that means!). Then Windows installed -- and of course booted by default only into windows.
The second problem was that BIOS-selected ubuntu booted, but to a mere desktop, without keyboard. In my case, what worked was to boot and run disk repair off the prepared memory stick. Rebooting after that, I got a familiar boot menu from grub, whence the ubuntu entry got me into the situation before installing windows (plus the ability to boot into windows). (I did not have to turn off UEFI video in the BIOS.)
My advice for windows(10)-after-ubuntu installation is to spend a few hours researching likely problems: this led me to this page, among others. Prepare (with unetbootin), and check (by booting it) a boot-repair stick.
Prepare (with the most up-to-date version of woeusb) a windows installation disk. When things do not work out, do not despair. Use your imagination, and wonder/research how your BIOS is involved. (Keep careful records of what you do: it may have to be backed out .. or maybe not.)
If things work out, consider donating to the unetbootin and woeusb projects. If not, they'll probably help out if you ask nicely, and then definitely donate. These projects give you a lot of your life back.