Start with the basics
Use sample cards and the rulebook for the variant you are learning. Sort by suit and rank, then explore different layouts without trying to finish quickly.
Put it into practice
Check each combination separately. Make sure the same card is not being counted twice and review any joker-related requirement. A neat arrangement is not automatically a valid declaration.
Before your next session
Try a second layout before deciding which one to keep. Write down the rule that makes a combination valid. This helps you identify what you still need to learn.