At lvl 69 I'm running a pure frost spec. It's very effective on mobs and 1v1 pvp.
Essentially you spam frost bolt. When Fingers of Frost/Frostbite procs, you can usually get off about 2 Ice Lances which are instant cast crits. I can usually nail 3-4 mobs one after the other before needing to evocate / mana up. Frost Nova is definitely your friend, and your water elemental helps a lot too, but I don't use it very often. Stay away from Cone of Cold as it eats mana, and if you DO use it, make sure it's against at least 2 mobs. Don't waste it on a single target. Also be sure to keep your Frost Armour up at all times (upgrades to Ice Armor eventually), and as soon as you get Molten Armour, use that as it boosts your crit. It's also helpful to apply Ice Armor if there are enemy players about, cuz if they attack you they will get a slowdown.
Check on WowWiki for some useful macros as well. One very useful one I use is for polymorph that focuses your target so you can keep an eye on him while you nail his budd(y|ies). Another one is a simple one for Counterspell.. just add in a /stopcasting before casting counterspell. This way you can interrupt your target even if you're in the middle of a long cast. Did the same for Ice Lance so I can get those crits in.
Essentially you spam frost bolt. When Fingers of Frost/Frostbite procs, you can usually get off about 2 Ice Lances which are instant cast crits. I can usually nail 3-4 mobs one after the other before needing to evocate / mana up. Frost Nova is definitely your friend, and your water elemental helps a lot too, but I don't use it very often. Stay away from Cone of Cold as it eats mana, and if you DO use it, make sure it's against at least 2 mobs. Don't waste it on a single target. Also be sure to keep your Frost Armour up at all times (upgrades to Ice Armor eventually), and as soon as you get Molten Armour, use that as it boosts your crit. It's also helpful to apply Ice Armor if there are enemy players about, cuz if they attack you they will get a slowdown.
Check on WowWiki for some useful macros as well. One very useful one I use is for polymorph that focuses your target so you can keep an eye on him while you nail his budd(y|ies). Another one is a simple one for Counterspell.. just add in a /stopcasting before casting counterspell. This way you can interrupt your target even if you're in the middle of a long cast. Did the same for Ice Lance so I can get those crits in.