We all have zombie days. Days when our head just isn't there. I just took the idea of zombie days literally.
Instead of saying, "I'm feeling a little out of it," I would close my eyes, stick out my arms and bump into walls, furniture and the occasional vase around the house while groaning monotonously. My mom did not enjoy zombie days.
Some days, though, your brain just isn’t working at full capacity. Maybe you didn't sleep well or you're worried about an impending visit from the in-laws, but you still need to play well enough for your partner to like you.
You can get away with playing like a zombie (eyes closed!) by following some good defensive principles. If you follow these “rules”, you’ll play… fine. You won’t be brilliant, but you aren’t too likely to do anything terrible.
There are two good rules to dictate your defense:
1) Second hand low, third hand as high as necessary
2) Don’t lead a new suit if you can help it
Sure there are other rules along the way ("Don’t lead an ace without the king," comes to mind), but if you follow these two rules in places where you have a decision, you’ll probably do well.
When you’re on your game, you can find some brilliant plays that go against these principles. Maybe you duck in third hand to maintain communication or play second hand high in order to get partner a ruff. You might attack a new suit because the opponents are threatening to take a lot of tricks in another suit or because you've worked out that partner's values must be in the new suit.
Generally, though, if you’re not sure and you default to these principles, you’ll defend as well as (or better than) a majority of the other players.
Take a look at this deal. You’ll be West and the dummy is North.
| Vul:None Dlr: S |
DUMMY
|
|
|
YOU
|
Auction:
| West | North | East | South |
|---|---|---|---|
1 |
|||
| Pass | 2NT* | Pass | 4 |
| All Pass |
*Jacoby 2NT: a four-card game forcing raise of spades
The play: The opponents bid quickly to 4. Declarer does not have a singleton. You lead the 
Q (when life deals you QJ109, you lead it). Declarer plays the 8 from dummy, partner plays the 6 (standard signals) and declarer the 4. First question: continue?
Yes. Partner's 6 seems like a high signal. Moreover, nothing about the dummy screams "danger!". You continue (probably best to play the 10 since partner "knows" you have the J, but you could also continue with the J if your partner is also having a zombie day) and everyone follows 7, 2, 4. Keep going?
Yes! This is going great! Let's try a third diamond. The trick follows K, A, 9. Declarer plays the K, partner discards the 
2. Declarer plays the Q, partner pitches the 
2.
Now another decision: declarer leads the 6. What do you do?
Current position:
|
DUMMY
|
||
|
YOU
|
Second hand low! There's a temptation to rise with the ace. Yes, dummy is always entitled to K, but you don't want to play your ace without capturing an honor. It's VERY unlikely that this is a singleton heart. Save it for when you can capture an honor.
The K wins (partner plays the 5). Declarer now plays the 8, 5 (partner), 7 and you win the 10. What now?
Don't break a new suit! This situation is what my mother would call a "two-for-one sale". You can force out two of the opponents trumps for one of yours. Play a spade (a suit that's already played). Another diamond would give up a ruff and a slough. Playing the A wouldn't likely be too terrible (declarer likely only has three based on the bidding and play so far), but just because you know that it will ruff out, doesn't mean that declarer knows that.
Declarer wins in their own hand (partner throws the last diamond). Last problem: declarer leads the 10. What do you do?
Second hand low! Don't play the queen here. If partner has the jack, they'll take it. If declarer has the jack, they might be "fishing" to get you to cover, intending to finesse the other way if you don't. Note that if you were declarer, you'd make it more difficult for the opponent to duck smoothly by leading the J (if you had AJ10, say). Declarer plays the K and A, lowing a trick to your Q on the third round. Down one. Good job! Were you brilliant? Not really. However, you didn't help declarer at any point. That's solid defense whether or not you're feeling 100%.
The full deal:
| Vul: None Dlr: S |
A5432 K8 K87 K76 |
|
| 874 A103 QJ109 Q43 |
J9542 A652 J852 |
|
| KQJ109 Q76 43 A109 |
Notice that if you play the A when declarer leads hearts, declarer can discard a club from dummy and make. If you switch to a club, declarer can guess the suit for no losers. As a defender, your job is often to make sure that you don't help declarer along the way. These principles will often aid you in that quest.