When a team member names trump they become the team's leader. As the leader, they have a plan. It's a losing game to try and out-think the leader(maker of trump). As the helper, it is your job to help where you can. Conversely, if you were to name trump, you would then take the lead. At the risk of repeating myself once again, this is a partnership game, it must be played as such.
In this hand the dealer sits in the North seat. His partner, in South, orders up the queen of diamonds. After placing the queen in his hand, the dealer discards the 9 of spades.
East starts the hand by leading the ace of clubs. The maker(S) trumps with the 10 and takes the trick. Their team has taken the first trick and one trump was played.
South knows that he will need his partner help. Even though his ace of spades is a singleton, he decides to save it until later in the hand. He leads the 9 of hearts and hopes that his partner will be able to take it.
It was starting to look as if things were going to go as planned. That was until third seat over-trumped North with the right. Now the opponents have taken a trick. They also have the lead. Three trump have been played.
East now leads the 10 of spades. The maker(S) thinks to himself, my ace should be good. Now the opponent, sitting in West, spoils the plan by trumping it with the ace. They now have two tricks with four trump gone.
West remembers that his king of hearts is boss and that by leading it he knows the maker's team it will need a trump to take it.
Here is where North needs to make a decision on what to do. Here is what he knows. Four trump have been played. He still holds one, for a total of five. The big question in his mind is 'what did my partner order on?' Here he has to assume his partner is counting on him to take a trick and has something to take the last trick. He takes the trick with the Queen.
If, your partner has ordered you and your team has lost two tricks. On the fourth trick, you must trump-in. This is assuming you will get the opportunity. Then it would be up to your partner to take the last trick.