Simply
1.Delphic focus and delphic lore
2. the grand invigoration buff with as many runes in it as you can find. right from level 1 there is no penalty for eating runes with this buff.
to really get into it, try this build guide by Chattius! The Shield Maiden - A Valkyrie from the land of Fire and Ice
It is possible to get regens down so low that you can chain cast any spell. but thats no always the best case.
thx