Red
mages should focus on their vitality and red magic stats before they
improve their staff. Most of the staffs under the Ultima staff have
very little difference between them really so first focus on getting
your vitality to 364 and your red to around 610 so you can wear Ultima
gear not including staff and have all but 2 of the skills. You should
be able to do this by level 90. After level 90, continue to boost your
red up to 700 to get meteor shower, the aoe leveling skill for red
mages, then begin to add to your strength and dexterity stats so that
they are 148 and 308 respectively. Now you have the necessary stats to
wear everything essential to a red mage including Vast Staff. Here you
have the option of either continuing to add to your vitality for better
jewelry, or adding to yellow skills to enhance your abilities. You will
also want to have Mana Barrier and Fire Fury and Wide Fury as your most
important master and transformation skills. The rest are at your
discretion.

Red Mages can also become Yellow Mages or a combination of the two.
Fire
fury available after level 100, can deal much more damage per hit than
any other class, sometimes enough to one hit a player. After level 160,
its Wide Fury, with buff, can guarantee almost 10k+ in damage ignoring
all defenses.

Though red mage's HP is low, after level 100, Mana
Barrier more than compensates for that weakness. Mana Barrier can take
off up to 70% of opponent's damage.

With Silence Aura after
level 160, Red Mage can continually drain the mana of surrounding
players in a massive circle. Silence Aura could mean death for other
mages and may disable Master Skill attacks of Blade, Fist and Archer.

Red
Mages can also use the skills of the Yellow Mage if they meet the
requirements. Place a green square skill into green slot in bottom left
and a blue square skill into the respected slot in the bottom left to
designate a main skill and a staff attack. Right click on target to use
magic attack, left click and hold to use staff skills.

To
use Master Skills (obtained after level 100) and Transformation Skills
(obtained after level 160) you first need to purchase skills from a
trainer.
See(Masters): Master Skills Quest Guide (link)
And(Trans): Transformation Skills Quest Guide (link)