On topic, though..
1.) Attrition. This is the #1 most important thing as a battlemage. You will heal faster, and usually out-damage your opponents faster.
2.) Area. The area you fight in is also VERY VERY important. Usually an area without water would be -best-, and an area with a lot of turns and twists is sublime. I've killed many people because thunderclap just ruined their day. Also, make sure you're always outside depending on who you're fighting. Never fight outside against an invoker.
3.) TIME. A biggy here. The time of day that you fight your opponent is BIG. 9-3oclock is best, getting the biggest and best sears as well.
4.) WHO you fight. You're going to have the most problems with berserkers and warriors, hands down. I've never really had problems with clerics or healers or even shamans, but decked warriors and berserkers will RUIN your day. If you're not in a cabal, and that big bad decked warrior wants you dead.. just simply don't fight him. (unless of course you have some other advantage up your sleeve..)
5.) nymph hearts, red and white staffs, green potions, bright red potions, Golden Flowers, ankhs and glimmering staffs, floating wands, ... make sure your consumables are caught up everytime you fight. If you don't have the consumables, don't fight.
6.) A good dancer. Best dancers in this game are: Divine Reckoning (good/evil/neutral and MAGIC) Shark's Maw (evil and BLUNT) Rib of Shudde Me'll (good/evil/neutral MAGIC) Master Forgeman's Hammer (neutral and BLUNT), notched axe (good/neutral and BLUNT), Soulblight (evil and MAGIC), and blood filled voulge (evil/neutral and MAGIC).
I'm sure there's others that have been added since, but those are good ones to look for.
ALSO MAKE SURE YOU TRAIN THE SPELLS AS YOU GET THEM. GOOD ONES TO TRAIN ARE: word of recall, sear, meteor swarm, control blades (these go up with use, actually, while the spells is active), dancing blade (MASTER MASTER MASTER.), air shield, terra shield, force field, reflective shield, blur, and even mana lock!