[loramin]

Simple approach: cast it on yourself first. When it runs out you'll know it's time to recast.

Of course, group buffs make this much easier, but it's viable with pretty much all Priest buffs, unless they're really expensive, you're casting them on the majority of the group, and/or you're already mana strained (e.g. from healing).

P.S. For tracking, just cast in group window order. Unless you're stoned or drunk you can remember who you buffed last, and whoever is next on the list (that needs it) gets it next.

If you don't know who is what class (so who needs what buff), that is worth taking a sec to get clear on when you join.