Been playing for few weeks.

Earning card can be a bit of issue, since there is no way to grind-too-much-gold, as the income is tied to the daily quests and wining game don't really reward anything.
Do daily quests > save enough gold > join competitive event to earn card/pack/gem rewards.

Don't spent gold on buying packs, save 5000 and join draft, you get more card that way, 48 instead of 40 even if you didn't win any match.
Plus you get minimum 50 gem.