Know what is wild
Your chosen format defines which cards can act as jokers. Read the rules before assuming that a printed joker and a selected wild rank work in the same way.
Explain the substitution
In the example below, a joker represents a missing card. Say exactly which card it stands for and check the resulting group. Moving a joker between groups can change more than one requirement.
Review without rushing
Check the other cards in each group after rearranging the hand. A familiar-looking layout should still be compared with the version’s pure-sequence and declaration requirements.
Practise the reasoning
Make a few sample groups with open cards. Describe what would happen if you used the joker elsewhere. Keep notes about any rule you need to check before the next session.
Look at the cards.
Here the joker stands for the 8 of spades. Check your variant’s joker rules.
These are individual combinations, not a complete declaration.