There are always times in games where you just can't seem to kill whatever beastie your are faced with. Dragon Age is fairly infamous for its impossible boss fights. But, they are not actually impossible. If you are determined not to turn down the difficulty and are trying to look for something to help you out, here are a few quick tips. These are applicable to most games actually.
1. If you have a save point before the battle, or in the case of Dragon Age 2 you are able to switch armor/weapons in the middle of a fight make sure you have the best armor and weapons equipped for your characters. I will go into what is best for who later, but if there are new items you picked up earlier in your quest and you haven't switched them out yet they can make ALL the difference in a fight that is close but you keep losing.
2. Use a healthy combination of potions and spells. Don't use a health potion until you absolutely have to. As a rule of thumb, heal first with spells and with potions second. If you have enough potions and the battle is long enough, kill time so that the mage's healing spell can regenerate. A few ways I do this is
-Taunt between two warriors if you have two in the group
-Pull the offending creature around to the other side of the battle ground
-Stun/paralyze said beastie
3. Make sure you have all of your buff spells activated. I know this sounds silly but sometimes things like this get neglected. With a game play style such as Dragon Age there should be NO reason for you to neglect anything like this. You have the ability to pause the combat and arrange anything you want (although you cannot stack spells any more to my displeasure)
4. Use choke points. If you are overwhelmed by enemies, pull them back to a smaller area. Area spells are best used when you enemies are clustered in one area, and can also mean life or death for your squishier teammates.
5. Kill mages first. You want to not be distracted by their 'tank' if it is a group attack. Also, focus firing down dangerous foes will make your life easier. Shift click to select more than one party member and point them towards an enemy that is causing a lot of damage.
6. Remember World of Warcraft? Don't just use characters because you think their commentary is funny, make sure that if you are going in for a serious fight you have a well balanced group. There are a lot of ways to do this but my primary build is very similar to a dungeon in world of warcraft.
Tank, dps, dps, heals: My character on my first playthrough is a two handed weapon specialist warrior, I also have Aveline with me as the 'tank' and then I always have one rogue in the group. Mages in Dragon Age do not have to just heal, so I usually have a mage with me who has a healing and some other damage tree, their mana is not as easily squandered as in some other games.
As far as dps goes, you can have melee or ranged. Typically you can count on ranged having less chances of being damaged in the fight (less healing intensive) but then you cannot use your second melee damage as a distraction as mentioned previously.
7. Do you really want to fight? In some cases you have the OPTION of fighting. If you are in a conversation with a potential fight, there is sometimes an alternate path. If you use your save points well (anticipate when you're going to go into a situation that may change the outcome of the game) you can reload and try to not get into the fight. Of course this depends on your play style, but if you know you are not well enough equipped for a fight don't pick it.
8. Watch for resistances. There is a very clear indicator when your spells are being resisted by a creature or boss. Try using something different, if you keep using something that is not effective you are just wasting mana and time.
9. Don't stand in the fire. Once again this is a lesson most people (well were supposed to) learn from world of warcraft. Don't step on traps, if you have a rogue they will tell you about them. Make sure to direct your party around traps, or and other damage causing area. Dragons breathe fire, make sure no one but the tank is in that area or you will have crispy mages.
