You don't need to know every meta comp. These 3 fundamental strategies cover 90% of beginner games and are applicable every patch.
Stay at Level 6-7. Each round, roll down to ~20g then save back to 50g. Goal: 3-star a powerful 1 or 2-cost carry. Very beginner friendly.
Save all game, hit Level 8 ASAP (usually by Stage 4-5), then roll for powerful 4-cost carries. Higher risk — you'll take damage early but spike hard late.
Roll aggressively at Level 4-5 to 3-star cheap units fast. Win streaks early, deal lots of damage. High variance but fun.