Mage builds abound on the Web for players of the MMO, Rift, but there's precious little I can find that tells prospective players about the class in detailed and complete terms. I'm going to try to do that, here. Each post will be tagged with "Riftmage" so you can follow that tag to find all of them.
Let me just spend a paragraph on those who don't play Rift yet: mage is one of the four "classes" or "callings" in the game (rogue, warrior and cleric being the other three). The diversity of the game comes from the 10 "souls" that these callings can arrange in any set of 3. If you've played World of Warcraft, then you'll be familiar with the idea of 3 talent trees. That's what your selected 3 souls look like in Rift, but you can select any 3 out of the 10 you like. This means that when I say, "mage", I can mean a necromancer who summons a pet; a pyromancer who throws fireballs around; a chloromancer who heals their party or raid by doing damage to the opponent; or an elementalist who summons an elemental pet among others.
To start, I'm not going to go into any great depth on any one soul configuration. Instead, I'm going to touch on the things that all mages think about. Firstly: mana regeneration. Clerics and mages are so-called "blue bar classes". They have a mana pool and must do something to regenerate that mana or have a very brief contribution to any dungeon, raid or warfront. Mage mana regeneration comes in two forms: active and passive. For the most part, the power-houses of mana regen are Archon and Warlock. Having one of these souls isn't required, but if you don't have one of them, you'll have to think very carefully about what particular mana regeneration abilities your soul configuration provides.
Passive mana regeneration is what the Archon trait, "Exhilaration" provides. This trait returns 2.5% of your maximum mana every time you gain a spell critical hit. Thus, any soul configuration built around a high critical hit chance should think carefully about going into Archon for essentially infinite mana!
Active mana regeneration comes in two forms: offensive and internal. Offensive mana regeneration may require a specific condition like the Necromancer "Consumption" trait which grants them a spell of the same name to debuff opponents and return mana. Offensive mana regeneration might also take the form of Archon's Leeching Flames which is a damage over time spell which grants mana in return over its duration.
Internal, active mana regeneration, on the other hand, requires that the mage perform some action which doesn't affect the target, but returns mana. One example of this is Chloromancer's Empathic Bond, which returns mana when the target of their Synthesis buff is damaged. Another example is the Warlock ability "Sacrifice Life: Mana" which damages the caster, but grants mana in return.
There are several tradeoffs to be had, here. Passive mana regeneration is attractive because it doesn't require any changes to the mage's cast rotation. You simply benefit from the abilities which you already use. Offensive mana regeneration, however, allows you to continue damaging an opponent while gaining mana..
The least attractive are the active, internal abilities because they require that you put a non-damaging spell into your rotation, consuming cast time that could have been used for other abilities. For healing, this might be attractive because a break in the action doesn't have to be filled with extra damage in order to win. Also, for damage over time-based builds, damaging the enemy continues after a full suite of DoTs have been applied, so taking one global cooldown to cast Sacrifice Life: Mana isn't as damaging.
Bottom line: mages consume mana like a man dying of thirst consumes water. You need to bring powerful mana regeneration tools to the party in order to remain competitive with your teammates, no matter what build you use.