Build around what you find
Equipment can be Normal, Magic, Rare, or Unique. Random affixes support attributes, defenses, healing, potion effectiveness, elemental attacks, and individual skills. Unique equipment uses themed combinations and can have tradeoffs.
Read the whole tooltip. A named-skill bonus improves that ability, not every spell or attack, and it does not teach the skill. A strong damage roll may still be a poor exchange for protection you need.
Custom callings have loot too
Compatible equipment can roll bonuses for Blue Mage techniques, Red Mage attacks, and Summoner offensive abilities. Examples include Aqua Pulse, Venom Fang, Arcane Thrust, and Crimson Reprise.
The possible bonuses depend on the item and its supported jobs. Every skill is not available on every piece of gear. Lantern Glass draws from the same bonuses when it reshapes an item.
Quality and strength are different
Affix strength improves through progression. T6 is the lowest affix band and T1 is the highest: a smaller tier number means a stronger band.
Rarity and affix strength are separate. A Rare item can have modest rolls, while a focused Magic item can fit your build well. Compare its underlying weapon or armor stats as well as the extra bonuses.
Seek better opportunities
Magic, Rare, and Mythic monsters offer better equipment-quality opportunities when equipment drops. No monster tier guarantees a Unique item.
Shape it with Lantern Glass
Lantern Glass changes the affixes on Magic and Rare equipment: Clear Glass makes Normal equipment Magic, Amber adds an affix, Crown makes it Rare, Ember adds more to a Rare item, Shattered rerolls every affix and Still rerolls only the numbers. The item keeps its identity, refine, cards and runes, and its own level decides how strong the affixes can be.
Equipment you don't want can be salvaged at the Workshop for Rune Dust and more glass. See The Workshop for the details.
Make the item your own
Cards, refinements, rune sockets and Lantern Glass provide additional ways to improve gear. Rune sockets are separate from card slots and preserve existing affixes.
The database describes base items and sources. Your item's in-game tooltip includes its particular rolls and upgrades, so use both when comparing equipment.