Your partner and you are in it together, you are a team. The success or failure of your team is dependent upon how well you listen and respond to each other through your play.
The first goal of the player who declares the bid is to protect their partner’s nil. Making the bid is always secondary to protecting the nil. Your team cannot make forward progress on the scoreboard if the nil is set, so protecting that is the first priority.
Covering your partner starts with your bid. Don’t be reckless. Consider everything carefully — the score, the consequences of failing to make your bid declaration, the likelihood of the success of your nil, among other things.
When play begins, if you are covering the nil, pay attention to where the cards are and where your partner’s nil may face difficulty. Your job is to cover that nil to the best of your ability given the cards you are dealt.
If you are nil and you know before the first card is played in that hand that you are set, except for particular reasons not to, you should show your partner that you are set and doing so in a way that does not provide cover to the opposing team.
The most direct method is to just take the first trick. Otherwise, to signal your partner that your nil is set, rather than playing, say, your king of clubs under your partner’s lead of the ace of clubs, play something from low enough down that he will come back low and attempt to set the opponents’ nil. Play a higher club on the second pass.
The nil player has an equal responsibility to be paying attention to where the cards are so that in the event the nil is set, he can then assist his partner in making the bid, avoiding bags or setting the opponents’ bid and, if at all possible, their nil.
If you are the bid player, your job is to be watching so that you do not miss seeing immediately the significance of your nil’s play, whether nil is signaling set or, once set, might be of assistance in making your team’s bid or setting the other team’s bid.
Once your team’s nil is set or signaled set, both players work together to inflict the most possible damage on the opposing team while minimizing their own.
When your team’s nil is set, priorities shift. If the opposing nil is not already set, your goal is to set it, or to set their bid, or both.
Except in game hand, do not allow yourself to become reckless with the nil’s safety in attempts to set the opponents’ nil. Nils fail automatically with enough frequency that sticking to that simple rule of protecting the nil at all costs, regardless of bid set or bags, you and your partner will prevail in the game.
Keep track of the score. Being ahead or behind or tied at game hand significantly affects how much risk your team needs to take in order to prevail.