6. Spend Your Gems on Opening Chests
Imore.com let players know what they should spend their gems on:
There are a few sneaky freemium-style timers built into Card Wars, but don’t be fooled into burning up your gems for more hearts to keep playing or to retry lost matches. Instead, use your gems to open chests and get rare cards. Though it may be easy to default to the Algebraic chest since it has higher-rarity cards, that doesn’t necessarily translate to in-game value. Once you have a few heavy-hitting creatures from an Algebraic Chest, you can probably get by on the lower-grade Cool Chest.