Declarer plays not only their own hand but also the dummy hand. Before starting play it is vital to identify which cards will allow you to make entries into each of the hands, so you can lead from the appropriate hand in a suit when needed.
Imagine dummy holds the following cards in Spades: A Q 10. You hold in Spades: K J 9
You should win three tricks in this suit. However, a quick glance at this hand should tell you that there are various ways to play the cards. Whichever way you play will win three tricks. But different permutations of play will leave you making the next lead from different hands. This is where we need to stop and plan. Which hand do we think we will want to be leading from in future rounds?
Here are a couple of scenarios to think about:
a) You have decided that you want to win the lead in Dummy. If you decide that later you will want to win the lead back in your own hand, you would look to retain entry possibilities in hand. You would lead the A from dummy and follow with 9 from hand. This leaves you two possible entries back to your own hand from dummy. Because of the split of the cards, we also have one opportunity to return the lead with an entry in dummy.
b) You have decided you want to win the lead in Dummy, but you also want to retain the opportunity of further entries to Dummy. In this case you would win with Dummy’s 10 (playing 9 from hand). You now have two possible entries back to Dummy, with the opportunity of 1 entry to your own hand if needed.
Can you work out what would happen if you played A from Dummy and then J from hand?
You would have only one entry to each hand, destroying the opportunity of making 2 entries to either hand, if needed.