These tips may sound a bit obvious or you may know a few already, but I decided to put them up for anyone who wants to try out being a mage (either human or elf, doesn't matter) for maybe the first time or something in Origins. I tend to use this strategy myself.

Tip 1: Since you are a mage, you generally are the ranged figher in your group, so you don't really have to bother with Leliana or Morrigan or Wynne (I know it sounds sexist but they are all the ranged characters unless you change up Leliana) unless you plan on just being the healer of the group, then you can just leave out Wynne.

Tip 2: Set your Mabari to be a defender or passive, he'll stick to you like glue and make sure to knock down or stun anyone who gets too close, giving you a breather to run or change weapon sets. Alistair and Sten or the others will stick to you, but they have more power then the Mabari so should be in the middle of the fray, while the Mabari who specializes to have high constitution and knockdowns stays close.

Tip 3: If you plan on being a Blood Mage, also go for an Arcane warrior. You can have better armour and aracne warriors also have high constitution which helps when you are a blood mage. It also helps that being an arcane warrior lets you use more powerful armour and weapons to defend yourself based on your magic stats instead of physical stats when you use Combat Magic.
**NOTE: You can use any weapons and armour you want based on your Magic when you have learned the Combat Magic ability, but your attacks will be based upon your physical stats unless it is active. Having the Mabari helps keep enemies at bay as you activate Combat Magic after changing your weapon set mid-battle.

Tip 4: If you are going to be a Blood mage, also aim to have the 'animate dead' ability. That way, while you use blood control on the enemies you at least can bring back one (and only one) to fight if one of your minions falls or one of theirs fall and basically swarm your enemies with their own numbers.

As you can imagine, I find myself generally trying to be a Blood Mage and Arcane Warrior.