Unfortunately there are limited viable deck possibilities when you play with starter deck cards. I can recommend searching on youtube for the most recent beginner deck guides. Maybe focus on Fire, water, earth and death first - these tend to be easier than light and dragons.
The right placement is key. Always put a tank first, like living lava, serpent of eld, unicorn mustang or cursed windeku. After that, assemble your team according to the available mana - and maybe put a flight card at the end...
But f2p is a tough grind, you have to have 1000 Card Power to get to Bronze II in order to earn DEC. Therefore it takes some time to get there, even if you play every daily quest. I try this since last december - I regularly attend giveaways bu I'm just at 140 Power yet. So you should know that you're in the long run... Good luck on your journey young traveler and Cheerio :)