Quoting Saz from the BEST TIPS thread:
Yet another tip: do NOT change roles on spellcasters until you get all the top-level spells you want. Priests: do NOT change roles until you get your Vine magic! Wizards: do NOT change roles until you get your Stone magic! Specialize in these, if need be at first, until you are ready to change to a new role.
The exception to this, of course, is
Warlock, which allows you to learn all prior spell craft with no penalty. Still, it's probably a good idea to get quite a few spells under your belt before switching to Warlock, for then you're encumbered with learning a minimum of FOUR spell groups, not just two.
-Sazerac
So many wonderful tips in that BEST TIPS thread!
Wyv