How to build power effectively?

Hey there, I've been playing for maybe two weeks now and I've been close to breaking into Bronze 2 a handful of times now. Every time I do though, I start to butt against the power restriction to rank up. I'm wondering if there is an effective way to raise your power early on. I see that renting cards increases your power but that seems like it would only be a temporary solution (and doesn't contribute to your SPS earnings).
I know that once I break that barrier and start earning DEC from battles it will become a good bit easier to build your power and card collection, so I'm trying to break through that barrier at the very least.