Hey, been there too.
It was quite tough in the beginning to get above Silver league. But with enough practice and better cards you'll eventually go up.
What I also noticed is, that especially in the beginning of the season I still mostly keep on losing. So I only concentrate on finishing quests for the frist few days of a season and like to attack for ranking 3-4 days before the season ends.

Also you might take a look at https://beempy.com/static/sm_decks_ranking.html
Especially in the lower ranks good monster combinations are important to beat higher level opponents :)

Good luck!