Most cards are named after a specific god, with each god providing a different kind of gift. If you stick mostly to cards named after one or two Gods, you should do well.
Here’s what you can expect from each god:
Odin: Judgment and punishment in and out of battle.
Thor: Glory and spoils for victory in battle.
Loki: Revenge or spoils for defeat in battle.
Frigga: Resources and support.
Heimdall: Foresight and surprises.
Tyr: Great numbers for winning battles.
You generally should strive for a relative balance of card types. Ignoring a card type completely (such as Quests, Upgrades, or Battle Cards) won’t make you automatically lose, but it may cost you!