First, you have to decide that quitting is not an option, that pain is good,
and mentally shrink the hill down to a size that you can dominate in your
own mind.     That's why we pre-ride courses.  The hills get smaller each
time.  So don't let yourself get psyched out in advance.  Most people quit
long before they really have to.

Then you have all the technical things, like proper gear allocation.  I
don't use the little ring anymore except for dire emergencies.  All that
frantic spinning tires me out quicker than keeping it in second and making
it happen.

Sing to yourself

Count your breaths

Look only 4 feet ahead, and say "just 4 more feet, just 4 more feet, ..."

Enjoy it!  Nothing will burn you out faster than hating a hill!

Have somebody follow you up the hill to keep your mind off yourself, and
onto making it happen and staying ahead.

Watch weight allocation on really steep sections, know how to pull back and
down on the bars, or use the "rowing motion" to transfer upper body strength
to the cranks.

Mix it up.  Stand up to power over the tough stuff.  Sit and spin to recover
your breathing and heart rate.  If it's really steep, you may need to gear
*up, then stand up, and you get more bang for your buck, and traction too,
generally, than if you try to granny over it.

Real steep and loose stuff, I act rather gaily sometimes, and jam the seat
nose where the sun don't shine so it drives the rear tire into the dirt, but
allows me to lean out forward so I don't pop up the front tire.

Watch tire pressure.  Too low and you're pushing too much rubber.  Too high
and your tire wanders around with a mind of its own.

OK, *careful weight allocation* and choice of line are crucial to avoid the
spin out.  Keep enough weight over the rear tire for traction, and try to
steer the front tire onto something solid for the rear to grip.  When you
pull back on the bars, try to pull straight back and down, which drives the
rear tire into the ground and keeps the front weighted.  Don't run such a
low gear that
you'll easily break the rear free, but choose a low enough gear to make the
climb doable.  Practice the "sphincter-hold" position to see if it works for
you:  Benefits of standing without the complicated geometrics of a full
stand. For more on my personal style, see: "RR: Boy did I ever take a wrong
turn". Deja search might find it.

Relax your shoulders, drop your elbows, relax your jaws, neck and anything
else you may be unconciously tensing up, and then sing to yourself to take
your mind off the climb.

"Tie yourself" to an object up in front of you, and let that object draw you
up as if contracting a stretched rubber band.  Sounds like a silly zen game,
but try it.

Try the sway or wig-wag from side to side seated, and standing.

Stand up and dance on the pedals.

Find what works for you, use it, but always look for new tools to throw in
the bag.