Generally I level up 3 different ways.
I have one of my 3 human people go
Chemist-Wizard-Time-Summoner up til 99 (Particularly with a Mage Character)
another Squire-Knight-Monk-Lancer up til 99 (With the Badass Tank-Soldier)
and Squire-Archer-Theif-Ninja (With the agile, far moving rouge-like typr character)

I've noted that those combos work really well in building each character in their prospective class type and about by the time you reach 99 (If lvling those characters and Ramza all at the same time) They should have those job classes either mastered or nearly mastered and the other characters will already have several lvls in each of the classes as a cause of training at the same time.

And this works for any character, pending how you want them built.

For a non-typical class suggestion. Have Agrias LVL up in Holy Knight til she has it mastered, then move on to Knight, Monk, Lancer. and she will be one tough Cookie when she gets to LVL 99.

Sure there are some stricter ways (LVLing only as one class) but I like getting the skills as well in the process of lvling up.