The easiest way is to remove a couple (3-5) of blue mr runes and replace them with mana regen. If you want to replace some armor yellows with mana regen, you might need armor reds and/or one or two armor quints to make up for it.
Personally I use a page like this for Nami, but not for others like Sona. It comes down a lot to play style.
On Sona, you probably just want to replace a couple of mr blues.
Do you use hybrid pen marks?