What is maxing?
Maxing means to reach the highest values or caps for any of the 8 different stats. Stats can be increased and maxed by consuming different colored gems. Gems increase a stat by 1 permanently, when consumed.
Health and Mana gems, however, each increase permanently by 5, when consumed.
Where do I get gems from?
Gems can drop from:
Darza's Gods, Event bosses, Dungeon bosses, Darza
How do I max?
Once you are happy with your roll, you will be looking to max your base stats, this means excluding any equipment stat bonuses. A way to find out what your base stats are is to first, unequip all of your equipment, then compare those raw/base stats with your class's stat cap totals. The number difference between your base stats and your class's stat cap totals will be the amount of gems you will need to consume.
Example: The Archer's max Attack is 75. If my Archer has a base Attack of 59, then I would need to consume 16 more Attack gems to reach max Attack.
How can I tell when a stat is maxed?
The color. A stat's text and value will change to gold when completely maxed out.
What comes after maxing?
When you get to the 6/8 total maxed stats mark, you should aim towards getting the highest tiered gear (often called Tops) or even Untiered gear (usually shortened to UT) for your chosen class.
If you also have other character slots, it would be a good idea to use your strongest character to farm for gems, towards maxing the other classes; if your character happens to die, at least you'll have a back up to play.