All depends on the style YOU like to play.
Sneaky Assassin mage is great fun. My main is a sneaky assassin.
Main Skills:
- Archery (Overdrawn 5/5, Eagle Eye and power shot are a must. I use Elven bow, I prefer it to Heavy bows)
- Sneak (Stealth 1/5, Backstab and Deadly Aim)
- Illusion (Get Quiet Casting and Dual casting for Frenzy at high level. Master of the mind is nice also)
- Conjuration (Mystic Binding and Soul Stealer. Use mostly Bound bow and Summon Dremora Lord)
- Light Armor (Agile defender 1/5, Custom fit, Unhindered and Wind Walker. I use Elven Armor, boot and gloves with Nightingale Cowl)
Secondary Skills:
- Alchemy (Alchemist 5/5, Benefactor)
- Enchanting (Enchanter 5/5, Insightful, Corpus and Extra Effects)
- Smithing (Steel, Elven, Dwarven and Arcane)
- Secondary weapon
Note about secondary weapon: Some will choose Sword or Dagger, so they go One-Handed (Armsman 5/5). Another option is to go Shield on the left hand and Bound Bow on the right hand. When you dispel your Bound Bow, your shield is automatically equipped. So you can Bash straight Away, giving some time afterward to get away and keep shooting with your bow.
Use of Illusion/Conjuration: if you are surrounded by enemies that spotted you, then cast Frenzy. The one that keep coming at you, cast Summon Dremora or Flame/frost/Storm atronach. They will take care of the aggro in melee. Step back, equip your bound bow and shoot your enemies.