Order your cross skills!
It is vital to order your skills so that you have everything you need as you need it. Here is my preferred order:

Blizzard II: You will be doing lowbie stuff quite a bit thanks to roulette. Blizzard II gives you an AOE you would otherwise lack for off-DPS. This can speed up these runs for you.

Swiftcast: This ensures you will have Swiftcast for Halatali and beyond. This will also make sure you can swiftraise ASAP.

Virus: Placing Virus here means the earliest you have it is Haukke/Brayflox, which is a very good time to have it. You will likely still be the only person with Virus, and the debuff eases a lot of pressure.

Surecast: The first dungeon you will have Surecast access is Stone Vigil where you will need to make sure every heal lands because things there hit like a truck.

Eye for an Eye: As others have mentioned, this is mostly for end-game, and no one is gonna die or notice if you don't have it.