It sometimes happens that you get "out-of-sync" with your partner. This is most likely to happen the first time you play with someone, but it also happens with people who have been playing together for years. For example, you might be playing your cards to set the opponent, but your teammate is throwing away tricks in an attempt to avoid collecting bags. Your partner is not a mind-reader, so don't get angry when this happens! Instead, try to read the cards they are playing and look for clues as to their intent.
Here's a (replayer) example where the bids sum to 11 and I am hoping to set the opponents. Some players will never try to set when the total bid is at 11, while others will always try, and some will go either way, depending on the strength of their hand, and things that happen as the cards are played out. The video below shows how the first few tricks played out. I've annotated it with comments; just pause the video if you need more time to read these comments.
Our opponents take an early trick using the Queen of Clubs. This bodes ill for my hopes of setting, since that trick was probably not counted in bidding; it's less common to count the Queen when bidding. But I haven't changed my mind; I will still try to set.
Immediately after that, the opponent's Ace of Clubs is trumped by my teammate. That's good for an attempt to set; it probably means that a trick that our opponents depended on taking was lost. It's also a clue that my teammate is in sync with my plans to set.
However, immediately after that, my teammate's Ace of Diamonds is trumped by an opponent! At this point, I get concerned that we will get set. That Ace was surely counted when my teammate made his bid. If he has a weak hand, he may find it hard to make his bid.
You can replay the hand to see how it all worked out. By the 8th trick, our opponents had already made their bid, and setting was out of the question. At that point, my team's priorities were 1) to ensure that we made our bid, and 2) to avoid taking bags, if possible. (We succeeded!)
Notice how I was "reading" my partner throughout this hand. You can't always be sure what they are thinking, since you don't know what cards they have in their hand. But you can make educated guesses. You will win more games if you make an effort to stay in tune with your partner.