Start renting some cards out. They can be very cheap and will boost your power level so you can get to higher tiers. Higher tiers = higher DEC wins.
Very soon your wins will outweigh your costs (with me it was around 36 hours - and that's to cover the cost of cards rented for 7 days).
Here's a link to a recent article I wrote about renting cards. The rental system has changed slightly (for the better I think as rental is cheaper now) but the principles should still be the same.
https://peakd.com/hive-13323/@sbenbow/renting-cards-best-thing-i-have-done-newbie