I'm also new to SPT and am still learning every day. However, I did win a couple of 12 & 15 matches tonight:

12
Zintar Mortalis
Haunted Spirit
Twisted Jester

15
Tyrus Paladium
Silvershield Paladin
Centaur
Divine Healer

The strategy for the 12 Mana match came from a post I read by @luizeba:
@luizeba/best-low-mana-decks-for-newbies-12-mana-and-14-mana-splinterlands-new-player-guide-02

The 15 match win was based on some of my own game play experience. Well that and some random luck because you never know who you'll go up against in Splinterlands.

Congrats on completing your first Daily Quest. I look forward to them every day. Cheers!