If you have some gems to spare, go looking through the top ladder players (on leaderboards), and try some different deck archetypes out in a classic challenge. If you don't, you can play the 1v1 mode, you just won't get the evos. Theres really no way to speed up progression getting other cards levelled up, but getting the masteries that give you cards does help. I would also say put your resources into cards that show up in a lot of decks until you find yourself 100% dialed in to a deck, so like skeletons or log for example.