Firebolt and either icebolt or lightning bolt
Firebolt for its damage, and either icebolt or lightning bolt for speed. Lightning bolt you'll want a lot of balance to be good with it though.
Windmill and refine are higher priority, but that doesn't mean you can't rank anything else.
Just remember, ranking too many skills, especially stronger ones like combat mastery, final hit, thunder, and fireball, will give you a ton of CP, making it harder to find easy to kill boss/awful/strong monsters for windmill.
At rC+, refine requires fails to rank, and dex from ranged skills and some life skills will make it hard to fail.
-dex equips can help a bit though. The 36 dex from rank 1 refine is a really nice boost. Too get the ores, I just spammed metallurgy (get at least rank 9, so you can get 2 ores at once)