Bid, Pass, or Double

1. Responding to 1C:/1D: The hands you want to pass with are 3-4 counts. Those have enough values that the opponents are likely not to bid game. Or maybe not make it if they bid it. You aren't out trying to steal partscores. And you don't want to bid on nothing red, or you can go for your life.
  1.  S:Qxxxxx H:xxx D:x C:xxx 1D:-1S:
  2.  S:Axx H:xxx D:xxxx C:xxx 1C:-1D:
  3.  S:x H:J10xxxx D:xxx C:xxx 1S:-1NT
  4.  S:xxx H:QJxx D:xxxx C:xx 1S:-Pass
2. Bidding at the 5-level

Example: you hold  S:Jx H:Qxxxxx D:xx C:A10x

CHO RHO You LHO
1D: Pass1H: 1S:
3H: 3S: 4H: 4S:
PassPass?

You should bid, because partner has a stiff spade.

CHO RHO You LHO
1D: Pass1H: 1S:
3H: 3S: 4H: 4S:
DblPass?

You should pass, because partner has two spades.

Example: you hold  S:x H:AKJxx D:Q10xxx C:xx

You LHO CHO RHO
1H: 1S: 2S: 4S:
?

You should pass to show shortness in their suit.

Now if partner has  S:KQx H:Qxxx D:Axxx C:Qx, he will double. They are probably going down, and we are definitely not making.

If partner has  S:xxx H:Qxx D:AKxx C:Axx, he'll bid. You are making, and they probably are not getting hurt badly in 4S:.

Does this always work? No. But avoiding the five level with 2-2 in their suit is usually right.

3. Helping partner bid at the 5-level

You hold  S:xx H:AQ10xx D:KQxxx C:x.

You LHO CHO RHO
1H: 1S: 2S: 3S:
?

You should bid 4D:. Then partner with  S:x H:Kxxx D:AJ10xx C:xxx knows to bid 5H:, but with  S:x H:Kxxx D:xxx C:AJ10xx, he knows to defend 4S:.

Rule: when the auction is competitive and it looks as if one side may have to make a decision at the five-level, your new suits are not slam tries, but show your shape so that partner can judge the offensive vs. defensive value of his cards.

These bids "authorize" partner to outbid them at the 5-level, but don't force us to double them if we choose to defend.

If you have a very good hand and know it is your hand, you can cue bid in most of these auctions, provided you stay below game. For example

You LHO CHO RHO
1S: 2H: 2S: 3H:
4H:

creates a force on your side. They cannot play undoubled. In auctions where a cue bid is not available, for example,

You LHO CHO RHO
1H: 1S: 2S: 3S:
?
then some partnerships play that 3NT is a "cue bid" and sets up a force. Don't try this without partnership discussion.