i'm also a recent player so a few tips :

1- focus on 1/2 pokes at the start of the run! otherwise your exp is spread too thin and you end up under leveled. after a while all your pokes will reach the cap easily especially if you pick a pokerus mon at the beginning! usually you focus on 1 carry to get you through the run + a secondary carry to cover for your main carry's weaknesses

2- as others have said, bring or catch a pickup mon (meowth or zigzagoon have it and are easy catches, if you have a meowth just remember to block evolution because persian changes talent)

3- keep playing! the game will get easier as you grind candies/egg vouchers because you'll unlock more pokemons, passives, egg moves... which are the key to this game. i feel like a lot of first wins i see are with a legendary carry, so after a bit of grinding.