For starters, flood with penetrating oil (any good hardware store).
This should help loosen it.

Vise grips, etc. will damage things. Use them as a last resort.

Vise grips are handy. Also, a conventional pipe wrench helps (it
tightens the more you lean into it). Also, I find what are known as
"pump pliers" -- adjustable, helpful for the lighter jobs. The handles
are pretty long, and you can get some leverage.

To avoid the problem in the future, get a small tube of plumber's
grease (hardware store again), and lightly lube the threads on the hose
bib. Makes getting things both on and off MUCH easier. Also, a dab on
the rubber "O" seal on the hose makes for a better seal. You can
tighten and seal with nothing more than hand force.

If you end up destroying the fitting, there are replacement/repair
fittings available.