I think you mean the series called The Death Gate Cycle (1990-1994). It's by Margaret Weis and Tracy Hickman. (Also the authors of the Dragonlance series.)
Two characters introduced in the first book are Haplo, a 'Patryn', and Alfred (not his true name), a 'Sartan'. They both use variations of special rune magic which is more powerful than human (or elf or dwarf) magic, but they pass as humans.
Patryns tattoo themselves with runes, and can create effects by touching individual runes or by "completing the circle" by effectively making a circuit of runes. Sartan magic is performed by singing runes, or tracing them in the air, but can also involve dancing to make runes on the ground.
The first book in the series is called Dragon Wing (1990).
Ages ago, sorcerers of unmatched power sundered a world into four realms--sky, stone, fire, and water--then vanished. Over time, magicians learned to work spells only in their own realms and forgot the others. Now only the few who have survived the Labyrinth and crossed the Death Gate know of the presence of all four realms--and even they have yet to unravel the mysteries of their severed world...
In Arianus, Realm of Sky, humans, elves, and dwarves battle for control of precious water--traversing a world of airborne islands on currents of elven magic and the backs of mammoth dragons. But soon great magical forces will begin to rend the fabric of this delicate land. An assassin will be hired to kill a royal prince--by the king himself. A dwarf will challenge the beliefs of his people--and lead them in rebellion. And a sinister wizard will enact his plan to rule Arianus--a plan that may be felt far beyond the Realm of Sky and into the Death Gate itself.