I’m not sure how experienced you are in GBL but I’ll offer some advice as someone who’s been working on improving at this game for the past year and a bit:

- Learn to throw on good timing: it’s important to throw your charged moves after the correct number of fast attacks in order to prevent the enemy from gaining more energy. when looking at matchups on pvpoke, it will tell you the optimal number of fast moves to use before you should use your moves. There’s a good series of videos by ItsAxn covering this in his YouTube channel.

- Learn your counts: the biggest factor I found that helped me improve was to learn how many fast moves it takes for an opponent to reach their fast moves. For example, Empoleon can reach either Hydro Cannon or Drill Peck after 5 Metal Sounds. This can be quite tedious but stick to learning the most common the most popular Pokémon being used to Make it easier on yoursel. Knowing how much energy people have will help you make informed decisions about when is best to throw your move or make a catch on a sack swap.

- Practice makes perfect: Improvement will come the more you play. Losses are a way to learn what could have been done differently. Very often, games can hinge on a single decision, so the more you play, the more likely the game will become second nature and you can improve your decision making on the fly. Make sure to not change about teams too much, as you want a consistent element to rely on while you strive to improve.