Very well, fair enough. Ill give you a brief on how I play as a mage:
I always start out as a pure mage, wearing robes only. During lower levels magika regeneration and obtinaing the highest amount of magika is THE most important thing in my honest opinion.
To get the most out of your mage you want to study all the different schools and use them all to your advantage. It can get quite boring if you're only a destruction mage. Well to me at least.
Illusion- I think this is the single most powerful skill set in the entire game as it gives you ability to control other people in addition to casting thief related spells like muffle and invisibility. Being able to calm an angry NPC or throw a frenzy spell at a group of bandits and watch them kill each other is just plain awesome. But the only thing is you need to invest in all the perks and get your level to 100 for it to be most effective. Its either all or nothing.
Conjuration- As a mage especially at lower levels is your best friend. Being able to summon a minion or two (at higher levels) is great for the simple fact that they will draw the attention of your attacker(s) away from you while dealing damage themselves giving you the opportunity to do other things. Conjured weapons can be a great thing as you can pick the perk that casts soul trap as you make your kill, in addition to being able to deal some high damage. Not to mention that say if you're using a bound bow, it will raise your conjuration level in addition to your archery level.
Restoration- A great school of magic for the simple fact that its worth investing just to get the necromage perk. This significantly increases the damage done to undead. Not to mention that wards fend off opposing mages magic in addition to blocking breath attacks from dragons.
Destruction- Is a touchy topic as some people think its underpowered on high leverls like Master and Legendary. I always get my Destruction cost down to 0% through means of enchanting. ANd by focusing mainly on conjuration and illusion, I never really have to use destruction, but only as a last resort if an enemy happens to get through my conjured minions. Duel casting destruction is extremely powerful. Like when you do it on a giant or a bandit chief along with the impact perk.
Alteration- Never really quite used it so Im sure someone else will chime in on that one.
Enchanting- By getting my enchanting level at 100 and picking the 5/5 perks and up the middle section of the skill tree, I always enchant gear focusing on destruction cost reduction. Destruction cost reduction at 25% x 4 pieces to enchant gives you 100% cost reduction. Nothing like being able to cast any type or strength destruction spell at 0 cost.
Once I get my enchanting up to 100 I usually make the switch to light armonr, simply for visual purposes.
Thats a good starting point I think. Im sure I missed some so I'll post if I can remember. Best of luck.