The first advice I would give you is to try the different initial setups (Belgian and German daisies). You start the game with 2 groups of marbles split across the grid.
Second is just to reach out to the other player and try to agree to both play aggressively. The game isn’t much fun for anyone if the game is a standstill for 30 min.
Unfortunately, defense is generally easier in this game. It has been a known problem in decades and, strictly playing by the rules, there isn’t much you can do if both players want to play defensively.