From my personal experiences:
First introduce them to free software that actually runs in Windows (VLC,
gimp, Libreoffice etc).
Once they are used to daily using this tools (this may take some time), show
them that by running gnu/linux they will use the same programs, only without
viruses, or "slothish" slow pc, no malwares...
Other hard thing to them is the Desktop environment. It takes time to get
used to. So I do not recommend you to present em with a DE much different
from that logical environment shipped with Windows (they are used to such
logic and it takes time to get rid of it). In that affair the modified Gnome
that is shipped with Trisquel is very fortuned! It does looks a lot like
Windows, at least for Windows users (Try showing Trisquel to a Windows user.
Ask this person to use your computer with Trisquel for 10 minutes. I tried
and got this answer).
Another approach is by acknowledging the difficult that some of them might
have with technology. Some people just don't like having to understand
everything or even don't have the will or patience to. Those people just want
a pc that ain't slow, have big buttons on one side of the screen which he/she
can just press and get what is wanted.
Sadly as it might be, there can't be a radical change in one's computer like
that. Try doing it progressively. It takes time. Maybe fully free software
only isn't the best way to start. Maybe begin with some non completely free
gnu/linux distribution (Quoting RMS (as well as I can remember): They will be
more free than those who use fully proprietary). I recommend Cinnamon DE as a
first DE to those who come from Windows. Luckily enough you will manage to
present your view to that persons.
Be aware: Not all everybody will understand your point, some may even believe
its foolish and childish. It is not. But be comprehensive; for learning is
not easy and teaching is very difficult.
