Personally, I think Umbrion makes for a better wall so I'd gather that the best way to go about Glaceon's learnset is to take advantage of it's special attack and pure Ice type and make a Pseudo-Legendary Grass/Ground Dragon buster for breaking through those big, bulky Pokemon like Dragonite, Venusaur, Garchomp, and Zapdos!
Glacion (M) @ Focus Sash
Ability: Ice Body
Modest Nature (+SpAtk, -Atk)
-Frost Breath/Ice Beam
-Hidden Power (Ground)
- Frost Breath: STAB and bypasses stat boosting defensive moves (Like
Light Screen/Calm Mind)
- Ice Beam: STAB, 100% Accuracy and has a chance of Freezing the target.
- Hidden Power (Ground): Covers Rock/Steel/Ground
- Shadow Ball: Support
- Wish: Delay/Healing
- Hail: Healing (If you have Ice Body)
A couple of options here: You can take advantage of the cover hidden power gives, but its power in Gen VI has been fixed to only 60 base SpAtk, so you could swap it with Wish/Hail.
If you can't get HP (Ground), Then (Psychic) is also acceptable as it covers Fighting and Poison types. You can also switch out Hail or Hidden Power for Substitute if you want, but I find that substitute is only really effective if you have a faster Pokemon, (or Trick Room active), which makes it not the best of choices for slow Glaceon.
(Battling Tip: Glaceon makes a great addition to any Trick Room Team!) =D