How to farm gems quickly and what deck to build now

I am a newbie, just installed the game 2 hours ago. I have Power of the Dragon structure deck, Gigantic Sparkle structure deck and 4820 gems. How can I quickly farm gems and what deck to build now? I want a deck that has cool artwork (dragon/...) and not too weak. I am thinking about Tenpai Dragon but I see people say that I would lose if I can't OTK opp.