Which races, birthsigns, classes etc benefit Mages?

Signs

The atronach sign is pretty nice, since it gives you so much magicka to cast spells. However, you won't be able to regenerate magicka by resting, you have to either absorb it from enemies or use potions.

If you dislike not being able to regenerate magicka while resting, the apprentice still give a good bonus to total magicka but is weaker against magic.

The mage sign will give you a small boost to magicka without any downside.

Details on signs

Races

The two most mage-friendly races are Bretons and High Elves. Honorable mention to the dark elves with a nice destruction magic for a more combat ready character.

Skill bonuses

• High Elves have better bonuses for a destructive mage with strong destruction bonus. They have a strong magicka bonus.
• Bretons would make good warmages, with strong conjuration and restoration bonuses. They have a moderate magicka bonus.
• Dark Elves have a good destruction bonus.

Starting stats

• Bretons have a slight advantage with 50 intelligence and willpower
• High Elves still do very well with 50 intelligence and 40 willpower
• Dark Elves have 40 intelligence and 30 willpower. Pretty bad for a mage.

Details about races

Class

I vastly prefer to custom make my class. For a mage, you would choose intelligence and willpower and choose magic as primary focus.

For the skills, you may want to not put all magic skills in your major and minor skills. Keep in mind that each level up in one of those skills will count as one point for your character level up, so try and have a balanced skill set so all of your attributes will have the chance to be raised.

As noted by Oxinabox, if you choose the Atronach sign, it is a good idea to take the alchemy major skill to be able to make potions to restore magicka.

Stats

Obviously, a mage needs high amounts of intelligence (which translates into magicka) and willpower, so an item that will give you a boost to any of those will benefit your mage.

Items that can give you temporary boosts are potions (made using alchemy. Items that can give you temporary or permanent boosts are wielded items with an enchantment (made using enchant).

My all-out in your face destructive mage would be as follows:

• High Elve
• Atronach sign
• Intelligence and Willpower bonus on character creation
• Magic skills focus
• Major skills: Destruction, Alchemy, Heavy Armor, Enchant, Speechcraft
• Minor skills: Athletics, Acrobatics, Restoration, Alteration, Mercantile

This character will start the game with pretty solid stats for burning your way through the beginning of the game. I prefer my mages in armor. Yes, they run slower, but they don't die as easily. There's a reason Telvanni do it.

NB. This is a naive way of making a class, and a character. While it may create a strong character at the start, on the long run you will have problems leveling and balancing your stats. Here is a very interesting and counter-intuitive read on how to make powerful characters.