How to play gladiator efficiently?

[Canadane]

You mentioned facing monsters away from allies... I did get a comment about this with the Ifrit trial... So there we go. Maybe that's what I've been missing, because prior to that, I never did it.

Thanks.

For Ifrit specifically you want him facing away from the group, with your back to the wall. This way he can't push you out of his range and everyone else is good to use their positionals.
Remember many melee classes need to know where the back and flanks of a target is going to be, and nobody wants the front facing them. Rarely do you see a frontal positional attack and it just avoids front facing cleaves.

The positioning of bosses and generally all mobs is one of the more important tank responsibilities. The others are not dying, and the super advanced tactic of not being slow.

Otherwise, you sound like you're doing dungeons with gladiator appropriately. Shield Lob into a couple flashes and then whatever combos you may have learned unless it's just some Total Eclipse spam because there's so many.
Gladiator is very simple to use until you reach Paladin levels, where it honestly doesn't get much more complicated but at least you have Shield and Sword oath. The guy asking a Gladiator to use an Oath should be chuckled at and taught when tanks learn their skills.

[BillyKaplan]

Total Eclipse

Isn't that a level 41 skill? They should be a PLD about that time already then.

Others covered most of what needs to be said, but what I usually do at the lower levels is Shield Lob, then Flash 2-3 times depending on how big a difference in level and gear there is between you and your party. Combo skills wise, alternate your targets and save your finisher and highest agro generator for the target the dps are focusing down, if such exist. To support AoE agro, and to at least keep from losing things to the healer if you have several enemies, I'd recommend using Flash again every other combo unless you see they're really ripping off of you, then use it more often.

[Canadane]

Isn't that a level 41 skill? They should be a PLD about that time already then.

46 in fact!
But nice catch, my bad.