I tended to rotate my party fairly regularly, depending on my mood. Everyone saw action from time to time.

I also tended to assign everyone an element, at least in the early game. They'd get that element's materia linked to an All for their main offensive spell.

Cloud=Lightning
Barret=Earth
Tifa=Ice
Aeris=Holy (though sadly, no direct Holy damage spells available, and I'm pretty sure Alexander was only found after she died, so I just gave her Cure linked to All)
Red XIII=Fire
Yuffie=Water (Mainly through Leviathan)
Cait Sith=Gravity
Vincent=Bio
Cid=Air

Everyone also had their particular Command Materia, but I'm going to have to think back on how I distributed those.