% chance to Hit with melee.
Every time you fight a mob you have a percentage to miss it depending on the difference between your level and the monsters level. So this stat will lower your chance to miss. For example, when fighting a mob equal to your level you have about a five percent chance to miss. Adding an extra one percent to hit will lower your miss rate to 3%. You will need about 16 hit rating for an extra one percent. Since mages don't melee though this isn't necessary.
% chance to hit with spells.
This works almost exactly like the chance to hit with melee. Each percentage will reduce your chance to miss with spells. But in addition your spells also have to deal with any resistances the mob might have. This stat is primarily used by mages and pure offensive casting classes when going against higher level opponents. It works like melee hit rating by reducing the chance your spells will be resisted by a percentage. You will need 22 spell hit rating for one extra percent at seventy. How much you ultimately need is determined by what you will be doing. If you are leveling you will only need at most five percent, but you can get by with a little less.

In PVP spell hit is a little less useful and you only need enough to cap out any enemy resistances. Five to seven percent is more than enough. For raids you will need much much more. When fighting a raid boss your should aim for 16% since they are three levels higher than you. Keep in mind, that there are a few talents that also help increase your spell hit rate by reducing resists.
+Dodge
This increases your chance to dodge a melee attack by a percentage. Tanks and DPS primarily use it though so there is no real reason to make it a priority. You need 19 dodge rating for one extra percent at seventy.
+Parry
This works like Dodge except that it lets you parry an attack with your weapon. Just like Dodge it is only worthwhile for front line fighters. You need 31 parry rating for one extra percent at level seventy.
+Melee Crit
Whenever you swing your weapon you have a chance of landing a critical strike. In addition to your crit chance from agility you can also get crit chance from armor as well. But melee crits are worthless for us so don't worry about it. You will need 25 crit rating for one extra percent at level seventy.
+Spell Crit

This works like melee critical hits but with spells. But instead of hitting for 200% damage like melee, spell crits hit for 150% damage. You need 22 critical strike rating for one extra percent at level seventy. As a mage you will usually want to get as much of this as possible. However, spell damage is still your number one priority. Critical strikes are random while spell damage is stable. Crits are also only really useful when you have a good bit of spell damage. Since a crit gives you an extra 50% damage, every point of spell damage is increased by 50% as well. Different builds will want more crit than others though. Frost builds especially want extra crit since they can double their crit damage and have a higher chance to crit against frozen targets. Arcane builds can also increase their crit damage but you will want an even match of spell crit and damage. It also depends on whether you will be doing nothing but arcane damage, or mix in some

elemental attacks as well. Fire builds also need critical strikes, but they have more talents that increase critical strikes so you can focus on more spell damage with your gear. Another problem with fire critical strikes is that a large portion of your damage comes from Ignite, which can be over written by another critical strike. So damage is usually better than crit when fighting for a long time.