The biggest word of advice I have for new gladiators has to do with point allocation. I didn't respec until I hit my late late 40s and did a 2:1 with Vitality and Strength. That helps clear the quest content a little bit easier. Remember that your primary focus is keeping hate. That'll feel hard to do early on but I promise it gets way easier in your mid to late 20s against large groups. Don't worry about marking targets religiously or anything, as you'll literally do your hate combo on one mob, turn to the next and do it again, and keep going in circles while popping Flash periodically. Again, you're not concerned with DPS or who the primary is. You're concerned with keeping hate.
Keep these things in mind and you'll be good :)
Current: FFXIV | EVE Online (again)
Former: FFXI | The Matrix Online (FOREVER!!!) | STO | SW:TOR | EQ2 | WoW | Florensia | RF Online
FFXI :: Valefor :: Dareknight, Darexius
FFXIV :: Valefor :: Dare Knight
EVE Online :: Dare Knight, Hazel Knight, Rex Knight