Free Gems - Hidden Areas
You will be able to find free Gems if you tap in hidden areas, these inlcude the street lights in the PvP Arena area, the trash cain in the Card Studio area, the fountain in the Gate area and the spinning card in the shop area.
Free Gems - Daily Login
Free Gems can be gained through daily login bonuses.
Duel Orbs
Collect this item whenever possible as they are used for making standard duelists appear in the world areas.
Summoning and Setting
The difference between summoning and setting a card is that setting a card places it in a defensive position, while summoning a card places it in the attack position.
Auto-Deck Building
If you use this feature it will fill your Deck with 20 cards. However, it is more beneficial to go through the deck yourself as it does not do a good job at builiding for complex battle strategies.
Purchasing Card Packs
Before you purchase card packs make sure you check out the kind of cards that are possible to earn in each set.
Monsters
Begin by having your Deck comprised of 1-4 star monsters and keep chipping away at your opponent while you build up to better monsters.
Spell Cards
Having a mixture of offensive spells, utility spells, and buff spells will enable you to have a variety of different moves which will ensure you are prepared for anything.
Trap Cards
Keep an eye on what cards your opponent has and use trap cards to counter certain attacks.
Duel School
If you are unsure about anything don't be afraid to check into the Duel School to consult the tutorials again.