General guidelines:
Attackers: CD or offense set with a CC, potency or health set as appropriate based on character's kit. Offense cross, crit damage triangle.
Tanks: Health/defense sets. Primaries vary based on kit; Kylo Unmasked does best with all health primaries, whereas Jedi Master Luke favors protection.
Support/healer: Usually speed/health sets with defensive primaries.
Almost everyone: as much speed as you can muster while adhering to the above guidelines.
These aren't hard-and-fast rules, as some characters do best with a "non-standard" setup. For instance, Droideka benefits from not having a ton of speed so it can do more true damage with its basic. General Kenobi should be modded for health if used under Padme, but does better with protection or defense under other leads.
Basically, read the kit and determine what the character's strengths are, then mod based on that.