Being that your lvl 25, you will want to focus on lvling. Frost is the best spec for lvling. Being able to do decent damage and keep your enemies at bay is what makes frost so viable for lvling.
For frost mages, there are a few talents that are NECESSARY to make it a viable grinding class.
Frostbite - 3 points. Causes a 15% chance for opponents to freeze from your chill effects.
Shatter - 3 points. Increases your critical strike chance by 50% against frozen targets.
Permafrost - 3 points. Causes targets movement to be slowed by an additional percentage.
Improved Blizzard - 3 points. Adds a chill effect to your blizzard spell. This is a must for AOE grinding.
There is also a talent that increases the critical strike damage by up to 100%. It is on the second talent tier and is attainable at lvl 15. This is also a must for frost mages.
When you hit lvl 60 you have a few options as far as specs go. Frost again is great for lvling to 80, but Fire and Arcane are now viable to lvl with.
If you want a good mix of pvp and dps I would go with arcane. Arcane is now by far the best in pvp. With a good spell rotation such as Arcane Blast and Arcane Barrage, the burst damage is extremely high. The only thing you would have to watch is your mana. Arcane tends to go oom much quicker than frost or fire, but with a few talent points and a glyph you can actually get up to 80% of your mana regen back while casting with mage armor active which is the highest in the game.