Your Arcanist Pet contributes about 30% of your overall damage. The exception is to never use Summon II (your tank summon) in a dungeon. You don't need the extra tank and should devote yourself solely to damage while in a party.

Also, generally speaking, your Ifrit summon is generally better for physical damage and against mobs, while the Garuda/Carbuncle summon is better against single targets. There are exceptions to these, and summoners generally have their preference, but don't be afraid to switch our your summon.

Also, use Virus before an enemy launches a massive attack (such as a limit break or similar attack from a primal). Virus doesn't cost you MP, but does have a long cooldown and renders the enemy immune to additional uses of virus for a short period (about 1 minute). If anything, it's more of a damage mitigation tool than anything else. Healers will generally use it, so you don't have to worry about it until the cutting edge of end-game raiding where you may actually talk with your healers about rotating virus on a raid boss.

A third point that hasn't been mentioned yet: You are the only dps role who can also raise. Even more importantly, you can swiftcast raise, and considering that arcanist is very mp-efficient, will have a surplus of MP to use it. Learn to swiftcast your raise. Your healers will thank you, your tank will thank you, and you will get a ton of commendations for saving everyone from a wipe.