The tongue does not touch the teeth, it makes firm contact with
the roof of mouth, pressing un the upper gums.
I think my /gli/ is good enough, but many Italians are just not capable
of saying it with the proper sound, it is one of the most diffucult sounds in
our language. Sorry, I can't explain any better!
Mr. Peachey is almost right , I would say the sound originates from the throat.