Tips for Advancing?

I'm trying to grind T5 to get some coins/cards. Dumped all trophies in lower and upper levels. Max trophies now 1298. Current trophies 325. Everyone I come up against has level 10 cards and I only have mostly level 8, and never get the cards I need to build up. What can I do?

Edit: Currently in Challenger III league. Never play tournaments as impossible to compete.