Two auctions came up today which sowed confusion, so I think they are worth mentioning.
First auction: LHO opens 1♣ and your partner doubles; RHO passes. You hold: ♠653 ♥109843 ♦J9 ♣1082.
You bid 1♥. LHO bids 2♣ and your partner doubles again. If you play support doubles—which I highly recommend—this should be a support double. Partner's takeout double of 1♣ has not suddenly metamorphosed into a penalty double of 2♣. Partner is showing three card support for your hearts. Just bid 2♥. [One way to think about take-out doubles: it is as if your partner opened ONE in any of the three unbid suits. If your partner had opened 1♦, you would have no trouble seeing that double as a support double.]
Certain conventions come up in almost every session of bridge which is why I recommend them: Stayman; Jacoby Transfers; Negative Doubles; Support Doubles; New Minor Forcing. Other conventions are lovely, e.g., Splinters, Michaels, Jacoby 2NT, etc., but don't come up very often.
Second auction: You hold ♠AKQ5 ♥964 ♦KQ874 ♣9 and open 1♦. It goes 2♣ on your left and pass by partner. 3♣ on your right. You pass. LHO passes and partner now doubles. What gives? Since partner did NOT make a negative double over 2♣, this double should be penalty. My apologies to Ruth Ng who made a good double, and I didn't leave it in. This is NOT a balancing situation (even though it feels like it) because partner had a chance to make a negative double earlier and declined. Incidentally, partner's hand is almost certainly four clubs with at least one trump trick and two quick tricks outside because your opening only promises two quick tricks.
The hand I enjoyed playing most I had ♠KQ75 ♥9 ♦AKQ5 ♣KQ92. I opened 1♦; LHO passed; partner bid 1♥; I bid 1♠ (no need to jump shift; partner should always raise with four spades and if partner has 5-6 points without a fit, we don't need to be any higher). Partner bid 2♠, so I raised to game. LHO led the ♠2 and I was looking at:
♠AJ93 ♥J764 ♦73 ♣1086
♠KQ75 ♥9 ♦AKQ5 ♣KQ92
Great discipline by partner to raise with any 4-card support hand! I took the ♠A on Dummy because I wanted to play a low club toward my ♣KQ92. To my shock, RHO showed out, by discarding a low club (upside-down attitude—he liked clubs). I led a club from dummy and he thought a moment and hopped up with ♣A and played the ♥K (King from ♥AKxxx in the middle of the hand, Mike) and then the ♥A which I ruffed.
Your goal is to cash as many winners as you can and eventually cross ruff. So, you take the top three diamonds, carefully discarding a CLUB from dummy when LHO follows to three diamonds. Then you cash a top club and play another top club. LHO fell from grace, ruffing with the ♠2—should have ruffed with ♠4 or ♠6 to force the nine. I overruffed with the ♠3 on Dummy. At that point, I can claim with a high cross ruff because I can ruff both hearts in my hand with the ♠KQ of spades and my remaining diamond and club will have the ♠J9 in Dummy behind LHO's ♠108. [LHO has three spades left and Dummy and I only have two each, but LHO gets no tricks.]
When defending a NT contract, you have lots of information about HCP. If Declarer is known to have 15-17, give her 16 (on average), add that to Dummy's HCP, your HCP, and subtract the sum from 40. Partner will be within one point (higher or lower) of that answer. With 1NT (15-17) on your right, you have: ♠A632 ♥64 ♦A1092 ♣K85. You pass; a Stayman auction ensues, and RHO denies a 4-card major. 3NT is final contract. You lead the ♦2 and are looking at this:
♠K984 ♥J10 ♦K97 ♣A962
♠A632 ♥64 ♦A1092 ♣K85
Declarer plays the ♦7. Partner plays the ♦8 and Declarer takes the ♦Q. Do NOT be fooled—Declarer has the ♦J. If partner had that card, she would have played ♦J, not the ♦8. Declarer plays the ♣Q; you cover, Dummy takes the ♣A and partner's count card shows an even number of clubs, surely two because declarer is attacking the suit. Now Declarer plays the ♥J from dummy which wins. Declarer next plays low spade to ♠Q. You take your ♠A and take stock. Dummy and you both have 11 HCP. Give Declarer 16. Sum is 38. Partner has 1-3 HCP. The heart play makes it likely partner has the ♥Q (or possibly the ♥K). Partner has indicated a doubleton spade, so the spade spots in Dummy are very ominous. Declarer is slated to take four clubs, three spades, three hearts and already has one diamond. If you play another low diamond, hoping for a miracle entry for later, Declarer will take 12 tricks. Cash your ♦A and take an average board.