To level up fast means getting to inferno as soon as possible or doing long chain runs (at least 9+). Buying those prayers that increase round scores help too. It's really not that difficult to level up. I have 3 characters at max before I stopped after the platinum (Elf, Wizard, and Sorc). Now, I just play with friends when they ask me. Anyway, the wizard has a great endgame where he starts hitting his stride around level 45+. During the times I did play with randoms, I did not meet one elf that could keep up with me DPS wise on both mobs and bosses. Amazons could only beat me if they used a Str potion so he is pretty devastating when played correctly.
Your core skills for maxing out are concentrate (fast recharge), spirit up (max hp), levitation (+50% dmg boost to all air attacks), slow (duh), blaze (main boss killer), and fire ward (+50% fire damage to all enemies inside the ward & be able to cast fire on water). Casting slow > fire ward > blaze along with UP + O is devastating. Of course, you can make it more ridiculous with a fire rod by jumping and spamming fireballs via evade cancelling. Add a strength potion and call it a day.
Other skills to have for sure are adroit hands to cast everything in quick succession, deep pockets (for spells and 2 rods), and evade. Now, evade is used to keep you in the air longer with levitate (evade cancelling) as well as to give the longest i-frames in the game when holding R1 on the ground.
The rest you can put into whatever you want. I choose extinction to clear out elite level mobs in one shot in Chaos lab. That spell can hit multiple enemies too and save a lot of time, but it is slow. It's best used with a sorc who has gravity. There are also those that put some into HP, but only put enough so that food gets you to 999HP otherwise it's a waste. Thunderstorm spell is useless because of thunderod's jump + O lightning storm attack. Same effect as the spell but with multiple casts and no skill points wasted. Storm is another viable option to clearing out mobs and doing mediocre damage to fire-resistant bosses. It's okay to use when there are a lot of wizards/demon imps spamming fireballs since pillars deflect.
Golem is useless outside of normal mode. If you have any skill points left over, one point in nutritionist is more than enough. Meteor swarm is too slow, but so worth it with coordination (with at least one sorc and one fighter). Sorc casts protection, fighter with 100% dmg increase to allies when shielding, strength potion for Wizard, and just laugh as most inferno bosses' life bars take about a 70% hit right off the bat. If no sorc, then use stalwart potions to cast uninterrupted if you decide to take meteor. Otherwise, blaze does a better job.