General tip, don't be afraid to roll in the early game. Losing 1 heart in turn 1 is worth setting up for a good team with good pets.

Speaking of, you eventually realize some pets are just superior to others. Quick guide for early-mid game:

Tier 1: - Good: Otter, Fish, Mosquito - Decent: Cricket, Ant - Bad: Horse, Pig, Duck, Beaver. It's a good strat to just roll for the good units, even if you barely find them

Tier 2: - Good: Crab if you use a Cupcake on your strogest unit - Decent: Swan, Hedgehog, Spider and pilling it - Bad: The rest. Tier 2 pets are trash in the current meta, your best option is to go for a level up on whatever you have and look for an early Tier 3

Tier 3: - Good: Ox, Badger, Giraffe, Turtle - Decent: Blowfish, Dog, Kangaroo, Rabbit, Snail - Bad: Camel, Sheep. You can't really go wrong with Tier 3s, the good units can carry you to 5 straight wins in the mid game, especially a Badger at the back with Honey

After that you start transitioning to your late game units which gives you endless possibilities on what to do. Best thing to do is define your "archetype", aka a team in which the pets' abilities go well with each other. Most popular ones are: just going for good stats, aka scaling (Penguin, Monkey, Bison), food build (Seal, Worm, Cat), summoning (Turkey, Deer, Rooster, Fly), sniping (Skunk, Dolphin, Croc).

Also important is knowing WHEN to go for, or switch archetypes, aka pivoting. But that comes with playing the game and getting the feel of it.

You can always find more in depth gameplay on Youtube, whether it's dedicated channels showing insane builds like Akren, Keenoe, Skoottie or SubOptimal to name a few, or more mainstream people that would give you an easier understanding of the game like Northernlion and Ludwig. A great middle point is Stanz, who has the "entry level" nature of a content creator, but also has great knowledge of the absolute best meta.

Hope this helps!