Artificer tactics

Ranged tactics

 * You are bringing solid crossbow DPS into quests. Try stay in close range in order to benefit from increased damage via Point Blank Shot. Improve your burst DPS with Endless Fusillade and/or runearm blasts.
 * When partying with melee characters, try not to kite monsters away from their melee range, they hate that.
 * As would be your combat role as any ranged character, wait for the tanks to engage, Intimidate, and pull aggro first before opening up with the crossbow and spells.
 * Additionally, using the Precise Shot Archer's Focus stance requires you to stand still to increase your damage, up to 25%. This means you need to figure out a good place to stand when all the mobs come out, to maximize your ability to turn the bad guys into your personal pincushions.  Stay back with the casters and other ranged characters; rely on your runearm to deal with the trash that gets by the tanks closer to you.  (Think of yourself as carrying an assault rifle or sniper rifle and a shotgun, and deal with your opponents accordingly.)update: precise shot stance no longer requires you to stand still
 * As always, target the enemy spellcasters first. Even though they tend to go down quickly, they are often in places melee characters can't get to, and are much more dangerous to the party.  Using your TAB key to scroll through and select available targets, along with your Precise Shot/Improved Precise Shot, helps immensely, especially as you will be shooting past and through melee characters and trash mobs to hit the casters, and follow up on other ranged enemies.

Spells
Artificers play similarly to wizards in terms of spells: they can offer a lot of buffs, and they can deal a lot of damage (especially at higher levels). Even with a maxed-out Intelligence and items that increase your mana pool, however, it is easy to run out of spellpoints quickly if you use spells irresponsibly.
 * Some buffs ought to be forgone entirely, such as Shield of Faith as most characters already have Protection items that offer like bonuses and therefore won't stack. Same with any ability score enhancement spell.
 * Ablative Armor is very useful for any character, easily warding against the physical damage of trash mobs, ideal for running into the thick of it and summoning a Flame Turret or casting another spell with a lengthy cast time before you get the Quicken metamagic feat.
 * Possibly one of your most effective uses of spell points is weapon infusions. Ranging from elemental to metal-based damage reduction-breaking to divine alignment to doubling the base weapon damage, infusing weapons is incredibly useful, and therefore wildly popular, for any combat class (melee or ranged), as you can enchant any weapon (melee or ranged) with extra damage sources (and they stack too: an electric Elemental Weapons buff will add another 1d6 electric damage to a default shock weapon).  You can deal a ton of elemental damage with a flaming crossbow with an electric-imbuing runearm and an acid buff at low levels.
 * Your curative admixture spells can emulate the effects of an equivalent Mass Cure spell, and similarly be used as splash grenades against undead. You can conveniently throw a cure potion to bring incapacitated players back to their feet (and if you're really lucky, you can even do this to yourself right before you get incapacitated).  Removing Curses, Diseases, and Poisons can very useful depending on the quest, especially if the majority of the party is identically afflicted, and saves on potions and spell points.
 * Electric spells are your offensive friends: Lightning Motes can render mobs more vulnerable to electric damage, Lightning Sphere is a nice AOE follow-up to Motes, and Blast Rod can wipe out anything that gets too close for comfort. Be sure to invest some Action Points into your electric spellpower enhancements and keep your eyes peeled for Magnetism items (consider crafting a Magnetism shard to your runearm if you can't find the space for such an item).
 * Blade Barrier, Tactical Detonation, and Prismatic Strike are all excellent crowd control spells.

Iron Defenders/Homunculus

 * Your iron defender can very easily take the role of a hate-tank while soloing low-level quests, much as any fighter or barbarian hireling might (and you get this guy for free!). However this is less effective at higher levels, so it is usually better to reset your pet's enhancements from using Intimidate, Trip, Sunder, and Fearsome Tactics to Bluff, Danger Avoidance, Skillful and Ruthless Deception, and Stealth Tactics, effectively transforming your dog from a standard tactical feat-using fighter into a sneak-attacking fighter-rogue hybrid.  The Homunculi Evasion capstone is also more useful against enemy spellcasters than the chance to doublestrike (obviously your iron dog cannot use ranged or thrown weapons so half of the Alacrity capstone is useless to begin with).
 * Your dog can also be a damage sponge if you haven't maxed his Adamantine Plating and Danger Avoidance, resulting in him being a spell point drain (much as low AC fighters and barbarians are to clerics). Of course, the best defense is not to get hit, whether by having a high enough AC to avoid being hit at all or by simply dropping the foe before he gets in range.
 * Overall your iron doggies are a useful asset throughout your journey to level 25. However, note that dogs are stupid and in some quests (especially end game/epics) they are often a liability (e.g. running off causing unwanted aggro). Please check with your party before calling your dog in a quest you are not familiar with.

End game raid tactics

 * As suggested by Shade in a forum thread, artificers are the ultimate scroll healers, able to cast heal scrolls at caster level 15 with +75 % effectiveness, for a total of 262 HP (before Healing Amplification).