Classes

There are three classes in the game. Hawke can freely pick from any of them at the start of the game. Hawke is the only character that can use multiple weapon types, can use all mage spell trees and has access to more then one specialization.

Warrior

Warriors can act as tanks and front line damage dealers. They use Strength to deal damage and Constitution to survive blows. Consider raising them with 2 Strength and 1 Constitution per level damage dealers. For a more tank based Warrior you may want to remove some points in Strength for Cunning. If you plan on using many sustained abilities at once, place a few points into Willpower.

The Weapon and Shield tree is good for both tanking and making use of cross-class attacks. Shield Bash with Pummel has a 100% chance to Stagger, while Scatter and Assault deal extra damage during Disoriented from a Rogue. Two-Handed Warriors will also want Mighty Blow and Scythe to follow-up any mage that manages to Brittle the enemy.

Any Warrior will want to have Taunt to keep the mages safe, though damage dealers won't really need to upgrade it. Tanks should make use of Turn the Blade, while damage dealers rely on Might (However both can be used at once). Battle Synergy is also a great means of helping tanks keep hate and reduce damage.

For Fenris be sure to get Vener of Calm, Battle Tempo and Inner Reserves. For Aveline consider Thickskin, Immovable and Bodyguard.

Rogue

Rogues can sneak around, fight with dual daggers, or shoot from afar with archery. Dexterity is the key ability to deal damage, though Cunning can help once scoring criticals. For archers try putting in 3 Dexterity each level (Though spending some in Cunning, Willpower and Constitution once in a while will help). For dual wielding Rogues consider 2 Dexterity and 1 Cunning (And of course some Willpower and Constitution now and again).

Archery users will want to upgrade Bursting Arrow with Shattering Arrow and Archer's Lance with Punishing Lance to deal extra damage to Brittle targets. Pinning Shot is also great for setting up Disorient. Dual-Wielders will want Merciless strike as their main attack, but Backstab with Murder is also very powerful.

Rogue can really help out the team by using Miasmic Flask, Chaos, and Overpowering Fog to keep the enemies under control. Both Speed and Precision from the Specialist tree have there uses, though Speed will come in handy more often. Because you should have a good Warrior tank, go for Blindside and Brand from the Scoundrel tree.

Isabela's Swashbucklers tree can transform her into a form of dodge tank, though it Experienced Hand is still good for damage. Varric's best skills include Well-Oiled, Embellishment, and Backlash.

Mage

Mages can serve as healers, supporters, or powerful damage dealers with area of effect spells. They will need Magic to boost their spells effects. For damage based Mages consider 2 Magic and 1 Willpower per level. If you plan on using many sustained abilities consider flipping it to 1 Magic and 2 Willpower. As always put a few points into Constitution (Especially if you go down the blood mage path for Hawke or Merrill).

From the Elemental tree you'll want to pick up Winter's Blast and Deep Freeze to set up Brittle combos. The same holds true in the Primal tree where you can gain Golem's Fist and Desiccate. Also spend a point in Rock Armor for your support characters. Both Spirit Strike and Walking Bomb are excellent choices for finishing a combo set up by a Rogue's Disoriented. Likewise, use Crushing Prison and Chain Reaction to end combos set up by a Warrior's Stunned.

Any mage should have Greater Heal, even if their main task is damage. Support mages should consider Valiant Aura, Elemental Weapons and Barrier to protect allies and boost damage. Glyph of Binding, Shackling Hex, and Death Hex are great means for debuffing enemy targets.

For Anders pick up Panacea, Regroup, and Aid Allies. Swift Justice is also nice as it is a passive skill. Merrill will have a greater support role when using Wrath of Elvhen and its upgrades. Blood of the First can also be useful if you have plenty of health to spare; Wounds of the Past is a great debuff for tormenting enemies.