This is a relatively easy character to play, particularly once you reach the higher levels. 3 mana / 2 defense each level is a good strategy, but every few levels you'll need to dump points into strength or dex because the better armor and equipment (which you absolutely need) usually has minimums.
For skills, max out ember lightning and critical strikes (plus equipment that provides bonuses to crit). With these two, you can hold SHIFT and click to attack remote enemies, even through walls and across chasms. It's almost too easy - the lightning bolts ricochet, attacking multiple foes, and with critical strike it's not uncommon to deal 1000-2000 hp of damage per hit.
The one thing to watch out for is getting mobbed. Even squads of weak enemies can be dangerous, because spells are interruptable, so having more than 3-4 enemies right next to you, particularly Fast (undead), can be suicide. It's also important to carry heal potions (you won't need mana) for the same reason - the Heal All spell is handy for reviving your pet, but only when things quiet down. It's too slow to save you if you get mobbed (and it's also interruptable).
Minions help a lot, particularly the two golems because they don't have a duration (they live until killed). The Summon Skeletons spell with some points in Charm Mastery can give you a squad of up to 5 re-summonable minions (the spell is cheap, and you just get in the habit of hitting the summon button every few seconds), and Flaming Sword gives you another (though shorter). Those plus your pet can keep any enemies far away while you deal the death.
Adventurer will help you level faster and make those potions more useful (necessary at high levels since there are only 5 potion tiers). Treasure Hunter is way more useful than you'd think, (maxing out at +25% gold/gear at level 34) as is Barter (60% at level 29). Having lots of gold and being able to buy cheap vendor goods when the 25% better drops aren't good enough means your gear will always be top notch and you'll never run out of 80% better potions.