I highly recommend if you're new, to work through it slowly and learn your class!

Lvl 6-7:
Goblin camp

Lvl 8:
Deliver letter Quest (From Cynthia in Tabor)
Kobold Pipe Quest (West of Shadow)

Lvl 8-10:
Rosinden Quest (Ekibi Caverns)
Both Muileann Quests (North of Shadow)
Piaf's Farm Quest* (North of Tabor)
DAILY: Demiplane*
DAILY: Rat Catcher (Shadow)
DAILY: Wailing Isle

Lvl 10-20:
Graez (Normal Undead Only)*
DAILY: Cultists and Wells (Aliki' Tah)

Lvl 15-20:
Ogre Caves (No Demons)

Lvl 20:
Pirates Cove
Githyanki Fortress

Lvl 20-25:
Azha Theatre Quest
Demon Part of Ogre Caves
Ogre Cave Quest
Graez (All Undead)*

Lvl 22-24:
Kill Minotaur (Graez)
Deathknight (Graez)
Turn in Axe Quest (Graez)
Lothwaite Spirit Quest

Lvl 25: Medusa (Graez)
Laerad Caverns Quest (Asgard)

Lvl 25-30:
Amazon Forest (Dallyh)
Crystal Tower (Seneca)*
Kinaro Caves*

Lvl 30-35: Dojo Quest (Asgard)
Hound Camp (Serakii)

Lvl 35:
Scarecrow (Serakii)
Arkhon (Under Kinaro)
Muln (Ice Island)
Dream Dragon (Ovadexel)
Geonslu (Tonerra)

Lvl 35-40:
Crystal Tower (Seneca)*
Dark Marsh

Lvl 38+:
Lava Tubes
Serakii Farms

Lvl 40-50:
Eldebaro Island

Lvl 41:
Lighthouse Quest (Graez)

Lvl 47+:
Tecqumin quest

Lvl 50:
Dallyh Marsh*

* = See Extra Notes at bottom of the section.

*Piaf's Farm Quest: Only do this if you have Fodder, can be difficult without.

*Graez Level 10 to 20: Only take on regular undead. Do not take on Greater Undead (Requires Death Ward Feat).
*Graez Level 20 to 25: Should be able to take care of all of Greaz undead.

*Pirates Cove and Torm: You are here to gather items for Wailing Island Quest. (What you need, you will have to figure out in game.)

*Daily Demiplanes: The exp from these are not great at lower levels. So I recommend just blowing throw them to kill the boss. I also recommend doing them in the later half of the 10 level blocks. So at level 10 you will be the strongest. Same with Level 20, 30, 40 and 50.

*Kinaro Caves: This one requires decent saves otherwise it will be rough.

*Crystal Towers Level 25 to 30: Do not take on the bosses at this level, just take on all the enemies within the Obsidian Staircase.
*Crystal Towers Level 35 to 40: Now you can make your way through and face all the bosses except for Intruder at the very top.

*Dallyh Marsh: This is one of the hardest places in the game. Requires melee class or caster class with knowledge. Mostly to help clear tax at this point and make money.

*Klauth: This is not for leveling, but to complete your journey and to gain the best gear, then this is what you will need.

*God Champions: The next step after Klauth are the God Champions to get greater loot.

*Leveling in a party adds some bonus exp gain, up to 4 members.
*Relics turned in by anyone in a party gives exp to all members of the party.
*Wailing Isle quests are short and easy, and exp scales with level.
*To get more in game help, type rumors, this command will list level appropriate areas and quests as well.

*If you are knowledgeable of the game, you can do some of these areas much sooner than listed. All the levels listed are if you are solo, new to the game, and don't have a great understanding of it and your class. Also being in a party helps you clear content faster and can do it sooner.

There is a lot more of the game to explore and the rumors command will show it. These are just the some of the more straight forward and simple places to get to and/or complete.

help rewards
reward <character name>

This gives usually around 5% a level to the person you reward, exp tax takes a cut of course.

Always nice to reward people for their time and RP!

Collecting relics requires game knowledge, and locations across the game. Though lots of time you can run into them or find them during quests.

At a 'Collector of Lost Relics' read list (This will display locations of relics for your level)
Go collect relic
return to collector
claim <relic>

1-10 Level Difference: No Penalty to slight.
11-15 Level Difference: Greater Penalty
16-20 Level Difference: Severe Penalty (Not Worth It)
21+ Level Difference: No Exp

*Quest Completion EXP does NOT get affected by this.

Thanks Eilistraee and Swus for help!